Add system diagnostics, power controls, and WiFi radio toggle to Tools tab (#389)

* Add system diagnostics, power controls, and WiFi radio toggle to Tools tab

Expands the web UI Tools tab with safe, purpose-built controls so users can
manage the Pi without SSHing in, instead of an arbitrary-command terminal
(the web UI has no auth and CSRF is disabled, so a shell would be unsafe).

- System Diagnostics card: renders the existing but previously-unused
  GET /api/v3/system/status endpoint (CPU, memory, temp, disk, uptime),
  with a manual refresh and a 10s poll.
- System Power section: reboot/shutdown buttons wired to the existing
  reboot_system / shutdown_system actions, behind a confirm step, with a
  dedicated powerAction() helper that treats the dropped connection as the
  expected "going offline" outcome rather than an error.
- Network Radio section: WiFi on/off toggle backed by new
  GET/POST /api/v3/wifi/radio endpoints and WiFiManager.set_wifi_radio() /
  get_wifi_radio_state(). Disabling WiFi is refused unless a wired
  connection is present (reusing the existing lockout guards), with an
  explicit force-off confirmation for advanced users.

No new privileged commands: uses nmcli radio wifi on|off (already
sudo-allowlisted) and the existing reboot/poweroff grants, so the
sudoers-alignment guard test stays green. Bluetooth toggle intentionally
omitted since the installer removes the BlueZ stack for LED timing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019X3he87Ggr1qt8y7mnFeuE

* Harden WiFi radio endpoint and diagnostics poll (review feedback)

Addresses code review feedback on the Tools tab additions:

- api_v3.py: parse the `enabled` POST field with the same string-aware
  coercion as `force`. A plain bool() cast turned {"enabled":"false"} into
  True (enabling instead of disabling) for any non-UI API caller.
- wifi_manager.set_wifi_radio() now returns a reason code alongside
  (success, message); the /wifi/radio error response includes it. The Tools
  UI only shows the force-off confirmation when reason == 'no_ethernet', so a
  genuine nmcli failure surfaces its real error instead of a misleading
  "no wired connection" prompt that would just retry into the same failure.
- tools.html: gate the 10s diagnostics poll on panel visibility
  (document.hidden / offsetParent), so switching to another tab stops the
  recurring /api/v3/system/status calls instead of churning the Pi off-screen.
  The initial load and manual Refresh remain unconditional.

Verified: {"enabled":"false"} now disables (refused w/ reason:no_ethernet),
{"enabled":"true"} enables; inline JS passes node --check; py_compile clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019X3he87Ggr1qt8y7mnFeuE

* Narrow WiFi-disable fallback except and add stack trace (review)

Addresses a CodeRabbit nitpick: the fallback handler in set_wifi_radio()'s
disable path caught bare Exception and logged without a traceback. Narrow it to
(OSError, subprocess.SubprocessError) — the errors subprocess.run realistically
raises — and log with exc_info=True for full context on the Pi. Anything
genuinely unexpected now propagates to the endpoint's outer handler (500),
matching the codebase's specific-exception convention.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019X3he87Ggr1qt8y7mnFeuE

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/wifi_manager.py

@@ -1883,7 +1883,96 @@ class WiFiManager:
         
         logger.warning(f"Failed to enable WiFi radio after {max_retries} attempts")
         return False
-    
+
+    def get_wifi_radio_state(self) -> Dict:
+        """
+        Report whether the WiFi radio is currently enabled, plus whether a wired
+        fallback exists. Used by the web UI's radio toggle so it can warn before
+        an action that could disconnect the browser.
+
+        Returns:
+            {
+                'enabled': Optional[bool],   # True/False, or None if undeterminable
+                'ethernet_connected': bool,  # wired fallback present
+                'available': bool,           # nmcli present / radio state readable
+            }
+        """
+        ethernet_connected = self._is_ethernet_connected()
+        enabled: Optional[bool] = None
+        available = False
+        try:
+            result = subprocess.run(
+                ["nmcli", "radio", "wifi"],
+                capture_output=True,
+                text=True,
+                timeout=5
+            )
+            if result.returncode == 0:
+                status = result.stdout.strip().lower()
+                if status in ("enabled", "disabled"):
+                    enabled = status == "enabled"
+                    available = True
+        except Exception as e:
+            logger.debug(f"Could not read WiFi radio state: {e}")
+        return {
+            'enabled': enabled,
+            'ethernet_connected': ethernet_connected,
+            'available': available,
+        }
+
+    def set_wifi_radio(self, enabled: bool, force: bool = False) -> Tuple[bool, str, Optional[str]]:
+        """
+        Turn the WiFi radio on or off.
+
+        Turning the radio OFF from the web interface is dangerous: if the device
+        is reachable only over WiFi, disabling it disconnects the very page that
+        issued the request. To prevent that lockout, disabling is refused unless a
+        wired (Ethernet) fallback is present, or the caller explicitly passes
+        force=True to acknowledge the risk.
+
+        Enabling reuses the hardened _ensure_wifi_radio_enabled() path (handles
+        rfkill soft-blocks + retries). Both directions rely only on
+        `nmcli radio wifi on|off`, which is already covered by the passwordless
+        sudoers allowlist (configure_wifi_permissions.sh) — no new privileged
+        command is introduced.
+
+        Returns:
+            (success, human-readable message, reason_code). reason_code is
+            'no_ethernet' when a disable is refused for lockout safety, or a
+            short failure code otherwise; None on success. The web UI keys on
+            'no_ethernet' to decide whether to offer a force-off prompt.
+        """
+        if enabled:
+            if self._ensure_wifi_radio_enabled():
+                return True, "WiFi radio enabled.", None
+            return False, "Failed to enable WiFi radio. Check logs for details.", 'enable_failed'
+
+        # Disabling — guard against locking the user out of the web interface.
+        if not force and not self._is_ethernet_connected():
+            return False, (
+                "Refusing to disable WiFi: no wired (Ethernet) connection was "
+                "detected, so turning off WiFi would disconnect you from this "
+                "page. Connect Ethernet first, or force it if you're sure."
+            ), 'no_ethernet'
+
+        try:
+            result = subprocess.run(
+                ["sudo", "nmcli", "radio", "wifi", "off"],
+                capture_output=True,
+                text=True,
+                timeout=10
+            )
+            if result.returncode == 0:
+                logger.info("WiFi radio disabled via web interface (force=%s)", force)
+                return True, "WiFi radio disabled.", None
+            logger.warning("Failed to disable WiFi radio: %s", result.stderr.strip())
+            return False, "Failed to disable WiFi radio. Check logs for details.", 'command_failed'
+        except subprocess.TimeoutExpired:
+            return False, "Command timed out while disabling WiFi radio.", 'timeout'
+        except (OSError, subprocess.SubprocessError) as e:
+            logger.error("Error disabling WiFi radio: %s", e, exc_info=True)
+            return False, "An error occurred while disabling WiFi radio.", 'error'
+
     def enable_ap_mode(self, force: bool = False) -> Tuple[bool, str]:
         """
         Enable access point mode