Drop the unused project description field entirely

It never got a UI home on the frontend -- removed from ProjectView a
few sessions back and never restored anywhere -- so it was a fully
live field (validated, stored, returned by the API, covered by tests)
with no consumer.

- Migration 011: ALTER TABLE projects DROP COLUMN description.
- ProjectRepository: description dropped from ProjectRow, SELECT,
  create() and update() -- update() is now just a rename (string, not
  a $fields array; there was never more than one editable field once
  this left).
- ProjectController: store()/update() no longer accept or validate
  it; update() drops the "provide at least one of title, description"
  branch, since title is unconditionally the only field now.
- Frontend Project type, root README's API docs and curl example.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -284,15 +284,14 @@ owner (the creator); another user's project — or a missing one — always resp
 | `GET` | `/api/projects` | the caller's projects, sorted A→Z by title |
 | `POST` | `/api/projects` | create a project |
 | `GET` | `/api/projects/{id}` | one project |
-| `PATCH` | `/api/projects/{id}` | update `title` and/or `description` |
+| `PATCH` | `/api/projects/{id}` | rename the project (`title`) |
 | `DELETE` | `/api/projects/{id}` | delete the project and its cards (`204`) |
 
 `GET /api/projects` is always ordered alphabetically (case-insensitive) by
 title; there is no other sort option. A user may own at most **100 projects** —
 creating one beyond that responds `409`.
 
-Create/update body: `title` (required on create, 1–255 chars), `description`
-(optional, ≤ 2000 chars, defaults to `""`). `PATCH` needs at least one field.
+Create/update body: `title` (required, 1–255 chars).
 
 Project representation:
 
@@ -301,7 +300,6 @@ Project representation:
   "project": {
     "id": 1,
     "title": "Website relaunch",
-    "description": "Q3",
     "owner_id": 1,
     "card_count": 3,
     "completed_count": 1,
@@ -452,7 +450,7 @@ curl -s $BASE/api/me -H "Authorization: Bearer $TOKEN"
 
 PROJECT=$(curl -s -X POST $BASE/api/projects \
   -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \
-  -d '{"title":"Website relaunch","description":"Q3"}' \
+  -d '{"title":"Website relaunch"}' \
   | tr -d ' \n' | grep -o '"id":[0-9]*' | head -1 | cut -d: -f2)
 
 curl -s $BASE/api/projects/$PROJECT/statuses -H "Authorization: Bearer $TOKEN"