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>

src/Support/Validator.php

@@ -90,6 +90,27 @@ final class Validator
         return $value;
     }
 
+    /**
+     * An integer (>= $min) or an explicit null. Only meaningful once has()
+     * has confirmed the field is present; a null return is a valid value.
+     */
+    public function nullableInt(string $field, int $min): ?int
+    {
+        if (!$this->has($field) || $this->data[$field] === null) {
+            return null;
+        }
+
+        $value = $this->data[$field];
+
+        if (!is_int($value) || $value < $min) {
+            $this->errors[$field][] = ucfirst($field) . " must be an integer of at least {$min}, or null.";
+
+            return null;
+        }
+
+        return $value;
+    }
+
     public function add(string $field, string $message): void
     {
         $this->errors[$field][] = $message;