Add Gantt chart view with card dependencies and start dates

Adds a new Gantt chart board view with custom SVG timeline rendering,
card-to-card dependency tracking with cycle detection, and a startDate
field on cards. Includes zoom controls (day/week/month), dependency
arrows, column-grouped task list, today marker, and real-time updates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/setup-rls.sql

@@ -78,6 +78,9 @@ ALTER TABLE custom_field_values FORCE ROW LEVEL SECURITY;
 ALTER TABLE automation_rules ENABLE ROW LEVEL SECURITY;
 ALTER TABLE automation_rules FORCE ROW LEVEL SECURITY;
 
+ALTER TABLE card_dependencies ENABLE ROW LEVEL SECURITY;
+ALTER TABLE card_dependencies FORCE ROW LEVEL SECURITY;
+
 -- ─── Tenant-scoped tables (direct tenant_id) ──────────
 
 -- Users
@@ -460,6 +463,28 @@ CREATE POLICY automation_rules_tenant_isolation ON automation_rules
     )
   );
 
+-- Card Dependencies (via blocking_card_id -> card -> column -> board)
+DROP POLICY IF EXISTS card_dependencies_tenant_isolation ON card_dependencies;
+CREATE POLICY card_dependencies_tenant_isolation ON card_dependencies
+  USING (
+    current_setting('app.current_tenant_id', true) = '__bypass__'
+    OR blocking_card_id IN (
+      SELECT ca.id FROM cards ca
+      JOIN columns c ON ca.column_id = c.id
+      JOIN boards b ON c.board_id = b.id
+      WHERE b.tenant_id::text = current_setting('app.current_tenant_id', true)
+    )
+  )
+  WITH CHECK (
+    current_setting('app.current_tenant_id', true) = '__bypass__'
+    OR blocking_card_id IN (
+      SELECT ca.id FROM cards ca
+      JOIN columns c ON ca.column_id = c.id
+      JOIN boards b ON c.board_id = b.id
+      WHERE b.tenant_id::text = current_setting('app.current_tenant_id', true)
+    )
+  );
+
 -- ─── User-scoped tables ───────────────────────────────
 
 -- Notifications