Make the inbox global instead of per-project

A card either sits in its owner's inbox (project_id AND status_id both NULL)
or belongs to exactly one project with a status in it (both set) -- enforced
by a CHECK constraint, never one without the other. The inbox is global to a
user now, not per-project: cards can move from a project into the inbox and
back into any status column of any project.

Backend
- migrations/009: rebuilds `cards` (SQLite can't relax NOT NULL / add a CHECK
  in place) with a nullable project_id, a new owner_id (cards need direct
  ownership once they can have no project), and the CHECK constraint. Cards
  that had no status (the old per-project inbox) move to the new global inbox.
  status_id's FK is now ON DELETE RESTRICT, not SET NULL -- nulling it alone
  would violate the invariant, and there's no status-delete endpoint anyway.
- CardRepository: "column" is now (owner_id, project_id, status_id); every
  method that dealt with a project's columns is generalised to also cover the
  inbox and cross-project moves (orderColumn, idsInColumn, repack, ...).
- CardController/routes: single-card and ordering routes move to global,
  since a card may have no project to nest them under --
  GET/PATCH/DELETE /api/cards/{id}, PUT /api/cards/order (body now takes
  project_id + status_id, both null for the inbox). New GET/POST
  /api/inbox/cards. PATCH no longer accepts status_id -- moving a card, in or
  out of a project, is exclusively PUT /api/cards/order now. A card created
  directly in a project (POST /api/projects/{id}/cards) lands in its first
  status, since a project card can't have no status.
- Tests: ProjectTest/CardStatusTest updated for the new routes; CardOrderTest
  rewritten with full inbox/cross-project coverage. 57 tests pass.

Frontend
- New stores/inbox.ts (the global inbox) and lib/cardOrder.ts (the shared
  PUT /api/cards/order call, used by both the sidebar and a project's board).
- AppSidebar: an Inbox section under the project list -- a vuedraggable list
  in the same "kanban" drag group as every project's kanban columns, so a
  card drags straight from the sidebar into whichever project is open, or
  back out. (The empty-inbox state needed a real bugfix: it wasn't rendering
  a <draggable> at all, so there was nowhere to drop a card back into an
  empty inbox.) A drop reloads the inbox and, if a project is open, its cards.
- ProjectView's kanban board drops its synthetic Inbox column -- just the
  real statuses now.
- DashboardView simplified to a plain grid of project tiles (name + card
  count); its per-project "New" section is gone, since a project card can no
  longer have no status.
- stores/cards.ts: patch/remove move to the global /api/cards/{id} routes.

Verified end-to-end against the rebuilt container (existing per-project-inbox
cards correctly migrated to the global inbox, 0 invariant violations) and the
dev server via headless Chrome: sidebar inbox -> project A "To do" -> back to
inbox -> project B "Done", full journey confirmed via the API at each step.

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

migrations/009_global_inbox.sql

@@ -0,0 +1,58 @@
+-- The inbox becomes global to a user rather than per-project: a card now
+-- either belongs to nobody's project (project_id AND status_id both NULL --
+-- sitting in that user's inbox) or to exactly one project with a status in it
+-- (both set). Cards also gain a direct owner_id, since inbox cards have no
+-- project to derive ownership from.
+--
+-- SQLite can't relax an existing NOT NULL / add a CHECK to a live column, so
+-- the table is rebuilt.
+
+CREATE TABLE cards_new (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    owner_id   INTEGER NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    project_id INTEGER NULL REFERENCES projects (id) ON DELETE CASCADE,
+    -- Was ON DELETE SET NULL; now that a project card must have a status
+    -- (the CHECK below), silently nulling status_id on a deleted status would
+    -- leave project_id orphaned without it. There is no status-delete
+    -- endpoint yet, so this is only a safety net.
+    status_id  INTEGER NULL REFERENCES card_statuses (id) ON DELETE RESTRICT,
+    text       TEXT NOT NULL,
+    complete   INTEGER NOT NULL DEFAULT 0 CHECK (complete IN (0, 1)),
+    position   INTEGER NOT NULL DEFAULT 0,
+    created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+    updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+    CHECK ((project_id IS NULL) = (status_id IS NULL))
+);
+
+-- Existing cards with no status were sitting in their project's old
+-- per-project inbox column; that concept is gone, so they move to the (now
+-- global, per-owner) inbox -- project_id cleared alongside status_id.
+INSERT INTO cards_new (id, owner_id, project_id, status_id, text, complete, position, created_at, updated_at)
+SELECT c.id,
+       p.owner_id,
+       CASE WHEN c.status_id IS NULL THEN NULL ELSE c.project_id END,
+       c.status_id,
+       c.text, c.complete, c.position, c.created_at, c.updated_at
+FROM cards c
+JOIN projects p ON p.id = c.project_id;
+
+DROP TABLE cards;
+ALTER TABLE cards_new RENAME TO cards;
+
+CREATE INDEX idx_cards_owner_project_status_position
+    ON cards (owner_id, project_id, status_id, position);
+CREATE INDEX idx_cards_status ON cards (status_id);
+
+-- Re-pack every column -- including each owner's inbox -- to a dense 0..n-1,
+-- preserving relative order. Safe despite writing the table it reads: the CTE
+-- is evaluated against the pre-update snapshot.
+WITH ranked (id, rk) AS (
+    SELECT id,
+           row_number() OVER (
+               PARTITION BY owner_id, project_id, status_id
+               ORDER BY position, id
+           ) - 1
+    FROM cards
+)
+UPDATE cards
+SET position = (SELECT rk FROM ranked WHERE ranked.id = cards.id);