feat: add standards wiki, MCP registry, and app template

standards_src/wiki/03_composition_root.md

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+# Composition Root
+
+## Summary
+
+All wiring happens in exactly one module. It builds a **flat resource
+registry** and exposes it to the HTTP layer and to scripts.
+
+---
+
+## The resource registry
+
+`init.py` returns a plain `dict[str, Any]`. Keys follow two conventions:
+
+- `<resource>_repo` — a repository adapter for a resource.
+- `<resource>_svc` — a service for a resource.
+
+Plus named infrastructure adaptors:
+
+- `http_cache_store` — response cache backend.
+- `progress_bus` — progress/event bus.
+- `<vendor>_<kind>` — fetchers, clients, stores.
+
+The API stores the dict on `app.state.resources` during lifespan startup.
+Handlers read from it; nothing imports concrete adapters.
+
+## Shape
+
+```python
+_resources: dict = {}
+_initialized = False
+
+async def init(settings=None) -> dict:
+    global _initialized
+    if _initialized:
+        return _resources
+
+    await setup_database(uri=settings.mongo_uri, db_name=settings.mongo_db)
+
+    # 1. leaf repositories
+    user_repo = create_user_repo()
+
+    # 2. dependent repositories (dependencies passed by keyword)
+    wallet_repo = create_wallet_repo(user_repo=user_repo)
+
+    # 3. services (build via the DI library, injecting the repo)
+    _resources["user_repo"]   = user_repo
+    _resources["wallet_repo"] = wallet_repo
+    _resources["user_svc"]    = get_user_service(user_repo)
+    _resources["wallet_svc"]  = get_wallet_service(wallet_repo)
+
+    # 4. infrastructure adaptors (optional)
+    _resources["http_cache_store"] = HttpCacheStore(...)
+    _resources["progress_bus"]     = ProgressEventBus()
+
+    _initialized = True
+    return _resources
+
+async def shutdown() -> None:
+    global _initialized
+    await close_stores(_resources)
+    await shutdown_database()
+    _resources.clear()
+    _initialized = False
+```
+
+## Typed accessors
+
+Expose a `get_svc(name)` helper with one `@overload` per key so scripts get
+typing without importing concrete classes:
+
+```python
+@overload
+def get_svc(name: Literal["user_svc"]) -> UserService: ...
+@overload
+def get_svc(name: Literal["wallet_svc"]) -> WalletService: ...
+
+def get_svc(name: str):
+    return _resources[name]
+```
+
+Also expose `get_db()` (raw database handle) and pure helpers such as
+`compute_fingerprint(payload)` (canonical hash used for deduplication).
+
+## Rules
+
+- `init()` is **idempotent**.
+- The composition root is the only place that imports concrete adapters.
+- Handlers never call `init()`; they read `request.app.state.resources`.
+- Scripts call `init()` / `shutdown()` around their work.