refactor: rename package fabledassistant -> scribe (code-only)

Renames src/fabledassistant -> src/scribe and all imports, plus the
default DB name and DB user/password (fabled -> scribe) in config +
compose. 952 refs / 154 files. Reverses the old 'internal name stays
fabledassistant' convention.

Code-only: live databases are still physically named 'fabledassistant'.
Deployed environments must set POSTGRES_DB / POSTGRES_USER (or rename the
DB) since the defaults now resolve to 'scribe'. Repo (FabledScribe), git
host (fabledsword), MCP (fabled-git) and the image name (fabledscribe)
are intentionally unchanged.

ruff check src/ clean locally; CI (typecheck + pytest) is the gate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/scribe/mcp/_context.py

@@ -0,0 +1,20 @@
+"""Per-request MCP context.
+
+The ASGI middleware (mcp/server.py) populates `_user_id_ctx` from
+scope['scribe_user_id'] before dispatching to FastMCP tool handlers.
+Tool functions then call `current_user_id()` to retrieve it.
+
+Tools must never fall back to a default user — `current_user_id()` raises
+if called outside a properly-authed MCP request.
+"""
+from contextvars import ContextVar
+
+_user_id_ctx: ContextVar[int | None] = ContextVar("scribe_mcp_user_id", default=None)
+
+
+def current_user_id() -> int:
+    """Return the user_id for the in-flight MCP request. Raises if unset."""
+    uid = _user_id_ctx.get()
+    if uid is None:
+        raise RuntimeError("no MCP user context — request was not bearer-authed")
+    return uid