refactor(ticket): migrate Ticket consumers to direct field access (Phase 1)

TIER-2 READ AGENTS.md, conductor/workflow.md, conductor/edit_workflow.md,
conductor/tier2/githooks/forbidden-files.txt,
conductor/tracks/tier2_leak_prevention_20260620/spec.md,
conductor/code_styleguides/data_oriented_design.md,
conductor/code_styleguides/error_handling.md,
conductor/code_styleguides/type_aliases.md before Phase 1.

Phase 1 of metadata_promotion_20260624: migrate Ticket consumers from
t.get('key', default) / t['key'] to direct field access (t.id, t.status, etc.).

Changes:
- self.active_tickets: list[Metadata] -> list[models.Ticket]
- _deserialize_active_track_result populates self.active_tickets as Tickets
- _load_active_tickets (beads branch) constructs Ticket instances
- topological_sort signature: list[dict[str, Any]] -> list[Ticket]
- Migrated ~40 consumer sites in src/gui_2.py: _reorder_ticket,
  bulk_execute/skip/block, _cb_block_ticket, _cb_unblock_ticket,
  _dag_cycle_check_result, ticket queue rendering, DAG panel
- Migrated ~10 consumer sites in src/app_controller.py: _cb_ticket_retry,
  _cb_ticket_skip, approve_ticket, mutate_dag, _push_mma_state_update_result,
  completed count
- Removed legacy Ticket.get() compat method (Task 1.5)
- Added tests/test_metadata_promotion_phase1.py with 15 regression-guard tests
- Updated existing tests to construct Ticket instances instead of dicts

Verified: 1885 of 1910 unit tests pass (25 pre-existing failures unrelated
to Ticket migration; many are live_gui/sim tests that need a running GUI).

tests/test_gui_kill_button.py

@@ -1,5 +1,6 @@
 import pytest
 from unittest.mock import MagicMock, patch
+from src import models
 
 def test_gui_has_kill_button_method():
  from src.gui_2 import App
@@ -36,7 +37,7 @@ def test_render_ticket_queue_table_columns():
   from src.gui_2 import App, render_ticket_queue
   app = App.__new__(App)
   app.active_track = MagicMock()
-  app.active_tickets = [{"id": "T-001", "priority": "medium", "status": "in_progress", "description": "Test task"}]
+  app.active_tickets = [models.Ticket(id="T-001", description="Test task", priority="medium", status="in_progress")]
   app.ui_selected_tickets = set()
   app.ui_selected_ticket_id = None
   app.controller = MagicMock()