feat(f3): Gate-F-Pflichttest bestanden — Minimal-Plugin NUR aus dem Guide gebaut

Der Pflichttest (Guide-Kapitel 29.1 verbatim nachgebaut) deckte 3 echte Guide-Luecken auf und wurde erst nach deren Behebung gruen: (1) __init__.py fehlte im Beispiel: discover_builtins scannt das Paket-Namespace und findet Klassen die nur in plugin.py leben nie. (2) Route brauchte vollen Pfad: main.py mountet Plugin-Router OHNE Prefix — leerer Route-Pfad wirft Prefix-and-path-cannot-be-both-empty. (3) Plugin-Routen werden dynamisch dispatched: sie erscheinen NIE in app.routes.

Alle 3 Luecken sind jetzt in Kapitel 29.1 mit Warnhinweis dokumentiert; tests/test_gate_f_minimal_example.py beweist dauerhaft dass ein Guide-faehiges Plugin funktioniert. Beweise: Gate-F-Suite 4/4 gruen; ruff clean; Cross-Plugin-Scan sauber.

docs/plugin-development-guide.md

@@ -1040,7 +1040,27 @@ describe('PluginRegistry', () => {
 
 ## 29. Examples
 
-### 13.1 Minimal Plugin
+### 13.1 Minimal Plugin (verified by tests/test_gate_f_minimal_example.py)
+
+> ⚠️ **Three pitfalls verified by the Gate-F test suite** — the original version of
+> this example failed all three:
+>
+> 1. **`__init__.py` is required** with a re-export of the plugin class —
+>    `discover_builtins()` scans the package namespace and never finds classes
+>    that live only in `plugin.py`.
+> 2. **The route must carry the full path** — main.py mounts plugin routers
+>    WITHOUT a prefix; an empty route path raises
+>    `Prefix and path cannot be both empty`.
+> 3. **Plugin routes are dispatched dynamically** — they never appear in
+>    `app.routes`; verify them via HTTP request, not via route introspection.
+
+```python
+# app/plugins/builtins/minimal_example/__init__.py
+"""Minimal Example plugin package."""
+from app.plugins.builtins.minimal_example.plugin import MinimalExamplePlugin
+
+__all__ = ["MinimalExamplePlugin"]
+```
 
 ```python
 # app/plugins/builtins/minimal_example/plugin.py
@@ -1069,12 +1089,17 @@ class MinimalExamplePlugin(BasePlugin):
 
 ```python
 # app/plugins/builtins/minimal_example/routes.py
+# NOTE: main.py mounts plugin routers WITHOUT a prefix — the manifest's
+# route path is documentation only. The full path must live here.
 from fastapi import APIRouter, Depends
 from app.deps import get_current_user, require_permission
 
 router = APIRouter()
 
-@router.get("", dependencies=[Depends(require_permission("minimal_example:read"))])
+@router.get(
+    "/api/v1/minimal-example",
+    dependencies=[Depends(require_permission("minimal_example:read"))],
+)
 async def list_items(current_user: dict = Depends(get_current_user)):
     return {"items": []}
 ```