fix(tests): resolve 17 persistent CI test failures (#15084)

Make the main-branch test suite pass again. Most failures were tests
still asserting old shapes after recent refactors; two were real source
bugs.

Source fixes:
- tools/mcp_tool.py: _kill_orphaned_mcp_children() slept 2s on every
  shutdown even when no tracked PIDs existed, making test_shutdown_is_parallel
  measure ~3s for 3 parallel 1s shutdowns. Early-return when pids is empty.
- hermes_cli/tips.py: tip 105 was 157 chars; corpus max is 150.

Test fixes (mostly stale mock targets / missing fixture fields):
- test_zombie_process_cleanup, test_agent_cache: patch run_agent.cleanup_vm
  (the local name bound at import), not tools.terminal_tool.cleanup_vm.
- test_browser_camofox: patch tools.browser_camofox.load_config, not
  hermes_cli.config.load_config (the source module, not the resolved one).
- test_flush_memories_codex._chat_response_with_memory_call: add
  finish_reason, tool_call.id, tool_call.type so the chat_completions
  transport normalizer doesn't AttributeError.
- test_concurrent_interrupt: polling_tool signature now accepts
  messages= kwarg that _invoke_tool() passes through.
- test_minimax_provider: add _fallback_chain=[] to the __new__'d agent
  so switch_model() doesn't AttributeError.
- test_skills_config: SKILLS_DIR MagicMock + .rglob stopped working
  after the scanner switched to agent.skill_utils.iter_skill_index_files
  (os.walk-based). Point SKILLS_DIR at a real tmp_path and patch
  agent.skill_utils.get_external_skills_dirs.
- test_browser_cdp_tool: browser_cdp toolset was intentionally split into
  'browser-cdp' (commit 96b0f3700) so its stricter check_fn doesn't gate
  the whole browser toolset; test now expects 'browser-cdp'.
- test_registry: add tools.browser_dialog_tool to the expected
  builtin-discovery set (PR #14540 added it).
- test_file_tools TestPatchHints: patch_tool surfaces hints as a '_hint'
  key on the JSON payload, not inline '[Hint: ...' text.
- test_write_deny test_hermes_env: resolve .env via get_hermes_home() so
  the path matches the profile-aware denylist under hermetic HERMES_HOME.
- test_checkpoint_manager test_falls_back_to_parent: guard the walk-up
  so a stray /tmp/pyproject.toml on the host doesn't pick up /tmp as the
  project root.
- test_quick_commands: set cli.session_id in the __new__'d CLI so the
  alias-args path doesn't trip AttributeError when fuzzy-matching leaks
  a skill command across xdist test distribution.

tests/agent/test_minimax_provider.py

@@ -341,6 +341,7 @@ class TestMinimaxSwitchModelCredentialGuard:
             agent._client_kwargs = {}
             agent.client = None
             agent._anthropic_client = MagicMock()
+            agent._fallback_chain = []
 
         with patch("agent.anthropic_adapter.build_anthropic_client") as mock_build, \
              patch("agent.anthropic_adapter.resolve_anthropic_token", return_value="sk-ant-leaked") as mock_resolve, \