feat(tools): manage the MQTT bridge and Pixlet editor from the Tools tab

PR #544's change, ported onto the api_v3 package split (#553). Identical
behaviour; only the placement of the new code differs.

The original added 508 lines to web_interface/blueprints/api_v3.py, which #553
deletes, so every hunk of it would conflict irreconcilably. Ported by AST:
26 new top-level items sorted to where the split puts each kind --

  __init__.py   2 imports, 11 constants, 7 helpers
  starlark.py   4 routes  (/starlark/editor/{apps,status,start,stop})
  misc.py       2 routes  (/integrations/mqtt-bridge{,/config})

Everything outside api_v3.py -- the Tools partial, the installer scripts, the
JS tests -- applied unchanged.

Routes: 111 from the split plus these 6 = 117, and the url-map snapshot is
regenerated to match, which is exactly what test_api_v3_url_map.py is designed
to make you do when routes are added.

Full Python suite: 4,278 passed, 68 skipped, 0 failed. The JS tests this PR
ships could not be run here -- node is not installed on this machine -- so
test/js/dom/test_tools_sections.js is unverified.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014RRtqXDCnvnY6EQwhT5CV9

test/fixtures/api_v3_url_map.json

@@ -315,6 +315,23 @@
    "OPTIONS"
   ]
  ],
+ [
+  "/api/v3/integrations/mqtt-bridge",
+  "api_v3.get_mqtt_bridge",
+  [
+   "GET",
+   "HEAD",
+   "OPTIONS"
+  ]
+ ],
+ [
+  "/api/v3/integrations/mqtt-bridge/config",
+  "api_v3.update_mqtt_bridge_config",
+  [
+   "OPTIONS",
+   "PUT"
+  ]
+ ],
  [
   "/api/v3/logs",
   "api_v3.get_logs",
@@ -747,6 +764,40 @@
    "POST"
   ]
  ],
+ [
+  "/api/v3/starlark/editor/apps",
+  "api_v3.list_pixlet_editor_apps",
+  [
+   "GET",
+   "HEAD",
+   "OPTIONS"
+  ]
+ ],
+ [
+  "/api/v3/starlark/editor/start",
+  "api_v3.start_pixlet_editor",
+  [
+   "OPTIONS",
+   "POST"
+  ]
+ ],
+ [
+  "/api/v3/starlark/editor/status",
+  "api_v3.get_pixlet_editor_status",
+  [
+   "GET",
+   "HEAD",
+   "OPTIONS"
+  ]
+ ],
+ [
+  "/api/v3/starlark/editor/stop",
+  "api_v3.stop_pixlet_editor",
+  [
+   "OPTIONS",
+   "POST"
+  ]
+ ],
  [
   "/api/v3/starlark/install-pixlet",
   "api_v3.install_pixlet",