fix(status-enum): add paused to ProjectStatus, validate, fix progress

Drift-audit Group 6 + Group 5 #6 (enum-extension / status drift):

- ProjectStatus gains 'paused' — routes and frontend already treated it as
  first-class, but the enum (the source of truth) omitted it and the error
  strings lied. A future CHECK derived from the enum would have rejected
  existing paused rows.
- create_project/update_project now validate status via ProjectStatus at the
  service layer (canonical gate; notes.status has no DB CHECK), so the MCP
  create/update_project path can't persist a typo'd status. MCP docstrings
  realigned to the 4-value domain; route error strings corrected.
- get_milestone_progress: cancelled tasks are excluded from the percent
  denominator (and now reported in status_counts), so a milestone whose only
  open task was cancelled reaches 100% instead of stalling below it.

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

src/fabledassistant/mcp/tools/projects.py

@@ -27,7 +27,7 @@ from fabledassistant.services import trash as trash_svc
 async def list_projects() -> dict:
     """List all Scribe projects for the current user.
 
-    Returns id, title, description, goal, status (active/archived), color,
+    Returns id, title, description, goal, status (active/paused/completed/archived), color,
     and a short auto-generated summary for each project.
     """
     uid = current_user_id()
@@ -142,7 +142,7 @@ async def create_project(
         title: Project name (required).
         description: Short summary of what the project is.
         goal: The desired outcome or definition of done for the project.
-        status: active (default) or archived.
+        status: one of active (default), paused, completed, archived.
         color: Optional hex colour for the project card (e.g. "#6366f1").
     """
     uid = current_user_id()
@@ -172,7 +172,7 @@ async def update_project(
         title: New title, or omit to leave unchanged.
         description: New description, or omit to leave unchanged.
         goal: New goal/definition-of-done, or omit to leave unchanged.
-        status: New status — active or archived.
+        status: New status — one of active, paused, completed, archived.
         color: New hex colour, or omit to leave unchanged.
     """
     uid = current_user_id()