docs: fix plugin config + store + dependency docs

PLUGIN_STORE_GUIDE.md
- 19 occurrences of port 5050 -> 5000
- All API paths missing /v3 (e.g. /api/plugins/install ->
  /api/v3/plugins/install). Bulk fix.

PLUGIN_REGISTRY_SETUP_GUIDE.md
- Same port + /api/v3 fixes (3 occurrences each)
- "Go to Plugin Store tab" -> "Open the Plugin Manager tab and scroll
  to the Install from GitHub section" (the real flow for registry
  setup is the GitHub install section, not the Plugin Store search)

PLUGIN_CONFIG_QUICK_START.md
- Port 5001 -> 5000 (5001 is the dev_server.py default, not the web UI)
- "Plugin Store tab" install flow -> real Plugin Manager + Plugin Store
  section + per-plugin tab in second nav row
- Removed reference to PLUGIN_CONFIG_TABS_SUMMARY.md (archived doc)

PLUGIN_CONFIGURATION_TABS.md
- "Plugin Management vs Configuration" section confusingly described
  a "Plugins Tab" that doesn't exist as a single thing. Rewrote to
  describe the real two-piece structure: Plugin Manager tab (browse,
  install, toggle) vs per-plugin tabs (configure individual plugins).

PLUGIN_DEPENDENCY_GUIDE.md
- Port 5001 -> 5000

PLUGIN_DEPENDENCY_TROUBLESHOOTING.md
- Wrong port (8080) and wrong UI nav ("Plugin Store or Plugin
  Management"). Fixed to the real flow.

PLUGIN_QUICK_REFERENCE.md
- "Plugin Location: ./plugins/ directory" -> default is plugin-repos/
  (verified in config/config.template.json:130 and
  display_controller.py:132). plugins/ is a fallback.
- File structure diagram showed plugins/ -> plugin-repos/.
- Web UI install flow: "Plugin Store tab" -> "Plugin Manager tab ->
  Plugin Store section". Also fixed Configure ⚙️ button (doesn't
  exist) and "Drag and drop reorder" (not implemented).
- API examples: replaced ad-hoc Python pseudocode with real curl
  examples against /api/v3/plugins/* endpoints. Pointed at
  REST_API_REFERENCE.md for the full list.
- "Migration Path Phase 1-5" was a roadmap written before the plugin
  system shipped. The plugin system is now stable and live. Removed
  the migration phases as they're history, not a roadmap.
- "Quick Migration" section called scripts/migrate_to_plugins.py
  which doesn't exist anywhere in the repo. Removed.
- "Plugin Registry Structure" referenced
  ChuckBuilds/ledmatrix-plugin-registry which doesn't exist. The
  real registry is ChuckBuilds/ledmatrix-plugins. Fixed.
- "Next Steps" / "Questions to Resolve" sections were
  pre-implementation planning notes. Replaced with a "Known
  Limitations" section that documents the actually-real gaps
  (sandboxing, resource limits, ratings, auto-updates).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/PLUGIN_REGISTRY_SETUP_GUIDE.md

@@ -95,14 +95,14 @@ Official plugin registry for [LEDMatrix](https://github.com/ChuckBuilds/LEDMatri
 
 All plugins can be installed through the LEDMatrix web interface:
 
-1. Open web interface (http://your-pi-ip:5050)
-2. Go to Plugin Store tab
-3. Browse or search for plugins
-4. Click Install
+1. Open web interface (http://your-pi-ip:5000)
+2. Open the **Plugin Manager** tab
+3. Browse or search the **Plugin Store** section
+4. Click **Install**
 
 Or via API:
 ```bash
-curl -X POST http://your-pi-ip:5050/api/plugins/install \
+curl -X POST http://your-pi-ip:5000/api/v3/plugins/install \
   -d '{"plugin_id": "clock-simple"}'
 ```
 
@@ -152,7 +152,7 @@ Before submitting, ensure your plugin:
 1. **Test Your Plugin**
    ```bash
    # Install via URL on your Pi
-   curl -X POST http://your-pi:5050/api/plugins/install-from-url \
+   curl -X POST http://your-pi:5000/api/v3/plugins/install-from-url \
      -d '{"repo_url": "https://github.com/you/ledmatrix-your-plugin"}'
    ```
 
@@ -311,7 +311,7 @@ git push
 # 1. Receive PR on ledmatrix-plugins repo
 # 2. Review using VERIFICATION.md checklist
 # 3. Test installation:
-curl -X POST http://pi:5050/api/plugins/install-from-url \
+curl -X POST http://pi:5000/api/v3/plugins/install-from-url \
   -d '{"repo_url": "https://github.com/contributor/plugin"}'
 
 # 4. If approved, merge PR