docs: replace stale API names, line numbers and the api_v3.py path

- ADVANCED_FEATURES: StreamManager methods that exist
  (get_next_segment, take_next_group, refresh, advance_cycle, ...), and the
  real on-demand status envelope ({status, data: {state, service}})
- app.py:199 / :144 / :607-619 line citations and
  web_interface/blueprints/api_v3.py (now a package) replaced with file and
  function names in ADVANCED_FEATURES, CONFIG_DEBUGGING,
  PLUGIN_ARCHITECTURE_SPEC, PLUGIN_QUICK_REFERENCE,
  PLUGIN_CONFIGURATION_TABS, TROUBLESHOOTING and web_interface/README
- CONFIG_DEBUGGING: partial /config/main saves change only sent keys; use
  /config/raw/main to replace the file; describe where validation runs
- TROUBLESHOOTING: clear_cache.py needs --clear-all (no args only prints
  usage)

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

docs/PLUGIN_ARCHITECTURE_SPEC.md

@@ -8,7 +8,8 @@
 > - Code paths reference `web_interface_v2.py`; the current web UI is
 >   `web_interface/app.py` with v3 Blueprint-based templates.
 > - The example Flask routes use `/api/plugins/*`; the real API
->   blueprint is mounted at `/api/v3` (`web_interface/app.py:199`).
+>   blueprint (`web_interface/blueprints/api_v3/`) is mounted at `/api/v3`
+>   in `web_interface/app.py`.
 > - The default plugin location is `plugin-repos/` (configurable via
 >   `plugin_system.plugins_directory`), not `./plugins/`.
 > - Example imports use `src/plugin_system/base_classes/*_plugin.py`;