fix(scripts): diagnostics follow the web autostart default and api_v3 package

#556 made a missing web_display_autostart mean "start" (only an explicit
false/off keeps the web interface down), but the diagnostics still said
otherwise: diagnose_web_ui.sh reported a missing key as "defaults to
false", diagnose_web_interface.sh said the web interface "will not start
unless this is set to true" and recommended enabling it, and
debug_web_manual.py printed False. Troubleshooting a down web UI pointed
users at a non-cause.

Both shell scripts now evaluate the setting with the launcher's own
autostart_enabled() (inline fallback if it cannot be imported) and report
on / off / not set (on) / unparseable config; debug_web_manual.py uses
the same function. They also check web_interface/blueprints/api_v3/
__init__.py: api_v3.py became a package in #553, so every healthy
checkout was reported as missing a file.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/debug/debug_web_manual.py

@@ -54,8 +54,13 @@ def main():
         config = config_manager.load_config()
         print("   ✅ Config loaded")
 
-        autostart = config.get('web_display_autostart', False)
-        print(f"   🔧 web_display_autostart: {autostart}")
+        # Same rule ledmatrix-web.service applies: only an explicit false/off
+        # keeps the web interface down; a missing key means on.
+        sys.path.insert(0, str(project_root / 'scripts' / 'utils'))
+        from start_web_conditionally import autostart_enabled
+        raw = config.get('web_display_autostart', '(not set, defaults to on)')
+        state = 'starts' if autostart_enabled(config) else 'will NOT start'
+        print(f"   🔧 web_display_autostart: {raw} (web interface {state})")
     except Exception as e:
         print(f"   ❌ Config check failed: {e}")
         traceback.print_exc()