feat(kanban): deadlines en cards (context menu, badges, calendario, history)

- migration 009 + columna deadline TEXT en cards
- backend: CardPatch.HasDeadline, eventos deadline_set/deadline_cleared
- KanbanCard: menu derecho con DatePicker, badge countdown con colores por ratio (azul>=50%, amarillo<50%, rojo<10%, red.9 overdue)
- App.tsx: filtro "Con deadline", handleSetCardDeadline optimista, jump-to-card + highlight
- CalendarView: popover por dia con seq_num + titulo, click navega a card en tablero
- HistoryModal: render eventos deadline_set/deadline_cleared
- .gitignore: *.log

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app.md

@@ -6,7 +6,10 @@ description: "Kanban board con persistencia SQLite, drag-and-drop entre columnas
 tags: [service, kanban, web, dnd-kit, mantine, sqlite, time-tracking]
 uses_functions:
   - random_hex_id_go_core
+  - parse_date_or_default_go_core
   - sqlite_open_go_infra
+  - sqlite_apply_migrations_go_infra
+  - sqlite_column_exists_go_infra
   - spa_handler_go_infra
   - http_router_go_infra
   - http_serve_go_infra
@@ -17,13 +20,26 @@ uses_functions:
   - http_error_response_go_infra
   - http_parse_body_go_infra
   - http_session_cookie_middleware_go_infra
+  - http_session_token_extract_go_infra
+  - http_session_cookie_set_go_infra
+  - http_session_cookie_clear_go_infra
   - password_hash_go_infra
   - password_verify_go_infra
   - session_create_go_infra
   - session_cleanup_go_infra
-uses_types: []
+  - percentile_int64_go_datascience
+  - duration_stats_go_datascience
+  - format_duration_ts_core
+  - format_datetime_short_ts_core
+  - string_hash_palette_ts_core
+  - color_bg_ts_ui
+  - color_border_ts_ui
+  - color_swatch_ts_ui
+  - fetch_json_ts_infra
+uses_types:
+  - DurationStats_go_datascience
 framework: "net/http + vite + react + mantine + dnd-kit"
-entry_point: "main.go"
+entry_point: "backend/main.go"
 dir_path: "apps/kanban"
 ---