Add per-project card statuses and a kanban board

Statuses
- Migration 006: card_statuses table (project-scoped) and cards.status_id, a
  nullable FK with ON DELETE SET NULL. Every new project is seeded with
  "To do" / "Doing" / "Done"; GET /api/projects/{id}/statuses lists them.
- New cards have no status -- they sit in an "inbox" until moved.

Project view
- Full-width and tabbed: "All tasks" (a flat list, sorted by name
  case-insensitively) and "Kanban" (Inbox plus one column per status).
- Drag a card within or between columns to reorder / restatus; the Inbox
  column has its own name + Add form.

Ordering
- Migration 007: `position` is now a dense 0..n-1 rank within a
  (project_id, status_id) column, not a project-wide order. New composite
  index idx_cards_project_status_position; existing rows re-ranked.
- PUT /api/projects/{id}/cards/order takes { status_id, card_ids } and sets one
  column's contents and order, re-parenting moved-in cards and re-packing their
  source column in a single transaction. PATCH status_id appends the card to the
  end of the destination column.

58 phpunit tests pass; the frontend type-checks and builds.

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

migrations/007_scope_card_position_to_column.sql

@@ -0,0 +1,24 @@
+-- `cards.position` was a project-wide sort key. It is now a rank *within a
+-- column* — the group of cards sharing a (project_id, status_id). The inbox
+-- (status_id IS NULL) is its own column. The "all tasks" view no longer uses
+-- position at all (it sorts alphabetically); ordering is a per-column concern
+-- driven by PUT /api/projects/{id}/cards/order.
+
+DROP INDEX IF EXISTS idx_cards_project_position;
+
+CREATE INDEX IF NOT EXISTS idx_cards_project_status_position
+    ON cards (project_id, status_id, position);
+
+-- Re-pack every existing column to a dense 0..n-1, preserving current order.
+-- The CTE is evaluated against the pre-update snapshot, so this is safe despite
+-- writing the same table.
+WITH ranked (id, rk) AS (
+    SELECT id,
+           row_number() OVER (
+               PARTITION BY project_id, status_id
+               ORDER BY position, id
+           ) - 1
+    FROM cards
+)
+UPDATE cards
+SET position = (SELECT rk FROM ranked WHERE ranked.id = cards.id);