refactor(mcp): drop fable_ prefix from tool names; rebrand to Scribe

MCP clients see tools namespaced by the server's local name already
(mcp__<server>__<tool>), so the fable_ prefix on every tool name was
redundant and ate tokens in the model's tool list.

Tools renamed (34 total):
  fable_search → search
  fable_list_notes / get_note / create_note / update_note / delete_note → list_notes / ...
  fable_list_tasks / get_task / create_task / update_task / add_task_log → list_tasks / ...
  fable_list_projects / get_project / create_project / update_project → list_projects / ...
  fable_list_milestones / create_milestone / update_milestone → list_milestones / ...
  fable_list_events / create_event / get_event / update_event / delete_event → list_events / ...
  fable_list_tags → list_tags
  fable_get_recent → get_recent
  fable_list_persons / create_person / update_person → list_persons / ...
  fable_list_places / create_place / update_place → list_places / ...
  fable_list_lists / create_list / update_list → list_lists / ...

Also rebranded in MCP scope:
  FastMCP("fable", ...) → FastMCP("scribe", ...)
  auth realm "fable-mcp" → "scribe-mcp"
  ASGI scope key fable_user_id → scribe_user_id
  ContextVar label fable_mcp_user_id → scribe_mcp_user_id
  Tool docstrings "in Fable" / "Fable task" → "in Scribe" / "Scribe task"
  Server _INSTRUCTIONS prose

Deliberately kept:
  - The internal Python package name `fabledassistant` (per project naming
    convention — internal stays).
  - "Fabled Scribe" as the official product/brand name (page footer,
    smtp_from_name default).
  - References to the legacy `fable-mcp/` standalone package in docstrings
    explaining what we ported from — accurate until that directory is
    deleted in Phase 10.

Client impact: existing MCP registrations need
  claude mcp remove <name> && claude mcp add ...
once with a freshly-copied snippet from Settings → MCP Access. Claude
Code then re-discovers tools on connect — old conversations that
referenced fable_* tool names will see "tool not found" on those calls
until updated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/fabledassistant/mcp/tools/search.py

@@ -1,4 +1,4 @@
-"""fable_search — semantic search across the user's notes and tasks.
+"""search — semantic search across the user's notes and tasks.
 
 Mirrors the existing fable-mcp contract so Claude's prior usage pattern keeps
 working. Differences from fable-mcp:
@@ -11,7 +11,7 @@ from fabledassistant.mcp._context import current_user_id
 from fabledassistant.services.embeddings import semantic_search_notes
 
 
-async def fable_search(q: str, content_type: str = "all", limit: int = 10) -> dict:
+async def search(q: str, content_type: str = "all", limit: int = 10) -> dict:
     """Semantic search over the user's notes and tasks.
 
     Args:
@@ -46,4 +46,4 @@ async def fable_search(q: str, content_type: str = "all", limit: int = 10) -> di
 
 
 def register(mcp) -> None:
-    mcp.tool(name="fable_search")(fable_search)
+    mcp.tool(name="search")(search)