refactor(mcp_tool_specs): delete redundant AGENT_TOOL_NAMES; use tool_names() at consumer sites

AGENT_TOOL_NAMES was a hardcoded snapshot of mcp_tool_specs.tool_names()
in src/models.py. The pre-existing test
test_tool_names_subset_of_models_agent_tool_names literally asserted
'tool_names() ⊆ AGENT_TOOL_NAMES' (proving the redundancy), and
AGENT_TOOL_NAMES was not maintained in lockstep with the registry
(it would silently drift if a new tool was added).

This commit:
 1. Deletes AGENT_TOOL_NAMES from src/models.py (replaced by an
    explanatory comment in the Constants section).
 2. Updates 3 consumer sites in src/app_controller.py:
    - 'for t in models.AGENT_TOOL_NAMES' -> 'for t in mcp_tool_specs.tool_names()'
    - (in 2 methods: __init__ + a setter)
 3. Updates 2 test sites in tests/test_arch_boundary_phase2.py:
    - 'from src.models import AGENT_TOOL_NAMES' -> 'from src import mcp_tool_specs'
    - 'AGENT_TOOL_NAMES' references -> 'mcp_tool_specs.tool_names()'
 4. Removes the tautology test
    test_tool_names_subset_of_models_agent_tool_names from
    tests/test_mcp_tool_specs.py (it asserted 'AGENT_TOOL_NAMES
    superset of tool_names()' which becomes meaningless after
    AGENT_TOOL_NAMES is deleted). Also removes the now-unused
    'from src import models' import from that test file.

Verification: VC9
  git grep 'AGENT_TOOL_NAMES' -- 'src/*.py' 'tests/*.py'  # 0 hits
  from src import mcp_tool_specs
  mcp_tool_specs.tool_names()  # returns the canonical 45 tools
  from src.app_controller import AppController  # uses the new path

Tests verified (15/16 PASS; 1 pre-existing failure unrelated to this
commit):
  tests/test_arch_boundary_phase2.py (6 tests; 1 pre-existing
                                          failure: test_rejection_prevents_dispatch
                                          is a dialog-mock issue that
                                          predates Phase 4)
  tests/test_mcp_tool_specs.py (10 tests; the tautology test was removed;
                                          the remaining 10 pass)

src/app_controller.py

@@ -27,6 +27,7 @@ from src.module_loader import _require_warmed
 from src import conductor_tech_lead
 from src import events
 from src import mcp_client
+from src import mcp_tool_specs
 from src import multi_agent_conductor
 from src import orchestrator_pm
 from src import paths
@@ -2106,7 +2107,7 @@ class AppController:
   saved = self.config.get("gui", {}).get("show_windows", {})
   self.show_windows = {k: saved.get(k, v) for k, v in _default_windows.items()}
   agent_tools_cfg = self.project.get("agent", {}).get("tools", {})
-  self.ui_agent_tools = {t: agent_tools_cfg.get(t, True) for t in models.AGENT_TOOL_NAMES}
+  self.ui_agent_tools = {t: agent_tools_cfg.get(t, True) for t in mcp_tool_specs.tool_names()}
   label = self.project.get("project", {}).get("name", "")
   session_logger.reset_session(label=label)
   # Trigger auto-start of MCP servers
@@ -2968,7 +2969,7 @@ class AppController:
   proj["project"]["auto_scroll_tool_calls"] = self.ui_auto_scroll_tool_calls
   proj.setdefault("gemini_cli", {})["binary_path"] = self.ui_gemini_cli_path
   proj.setdefault("agent", {}).setdefault("tools", {})
-  for t_name in models.AGENT_TOOL_NAMES:
+  for t_name in mcp_tool_specs.tool_names():
    proj["agent"]["tools"][t_name] = self.ui_agent_tools.get(t_name, True)
   self._flush_disc_entries_to_project()
   disc_sec = proj.setdefault("discussion", {})
@@ -3268,7 +3269,7 @@ class AppController:
   self.ui_auto_scroll_tool_calls = proj.get("project", {}).get("auto_scroll_tool_calls", True)
   self.ui_word_wrap = proj.get("project", {}).get("word_wrap", True)
   agent_tools_cfg = proj.get("agent", {}).get("tools", {})
-  self.ui_agent_tools = {t: agent_tools_cfg.get(t, True) for t in models.AGENT_TOOL_NAMES}
+  self.ui_agent_tools = {t: agent_tools_cfg.get(t, True) for t in mcp_tool_specs.tool_names()}
   # MMA Tracks
   self.tracks = project_manager.get_all_tracks(self.active_project_root)
   # Restore MMA state