feat(mcp): project + milestone CRUD tools

Seven tools matching existing fable-mcp contracts:
  - fable_list/get/create/update_project (no delete; archive via status)
  - fable_list/create/update_milestone (no get; no delete)

LLM-era similarity-check / 'confirmed' guard for create_project is
NOT replicated — Claude doesn't need it. The service's auto-summary
regeneration side effect (services.projects.update_project) stays
for now; gets removed in Phase 7 along with all other LLM code.

Notable sentinels:
  - update_milestone: order_index=-1 means "leave unchanged" (0 is valid)
  - create_milestone: description="" becomes None at the service layer

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

src/fabledassistant/mcp/tools/__init__.py

@@ -4,7 +4,9 @@ Each tool module exposes a `register(mcp)` function that attaches its tools
 to a FastMCP instance. `register_all(mcp)` is the single entry point called
 from `mcp.server.build_mcp_server`.
 """
-from fabledassistant.mcp.tools import notes, search, tasks
+from fabledassistant.mcp.tools import (
+    milestones, notes, projects, search, tasks,
+)
 
 
 def register_all(mcp) -> None:
@@ -12,3 +14,5 @@ def register_all(mcp) -> None:
     search.register(mcp)
     notes.register(mcp)
     tasks.register(mcp)
+    projects.register(mcp)
+    milestones.register(mcp)