chore: remove dead code — 28 unused functions/classes across 16 files

Vulture + per-symbol verification (whole-repo grep incl. tests, string
literals, getattr, decorator/registry/argparse dispatch) confirmed each of
these has zero callers anywhere — not reachable via any dynamic-dispatch path,
not referenced by tests, not re-exported.

Removed:
- acp_adapter/tools.py: _build_patch_mode_content
- agent/anthropic_adapter.py: read_claude_managed_key (diagnostics-only, never called)
- agent/bedrock_adapter.py: get_bedrock_model_ids
- agent/browser_registry.py: get_active_browser_provider
- agent/chat_completion_helpers.py: _take_request_client (x2 nested closures, never invoked)
- gateway/platforms/weixin.py: _rewrite_headers_for_weixin, _rewrite_table_block_for_weixin
- hermes_cli/banner.py: _skin_branding
- hermes_cli/debug.py: _delete_hint
- hermes_cli/gateway.py: _setup_email, _setup_sms, _setup_yuanbao
  (platform keys absent from the _builtin_setup_fn dispatch dict; handled by
  the _setup_standard_platform fallback)
- hermes_cli/kanban_db.py: set_max_runtime, active_run
- hermes_cli/kanban_diagnostics.py: severity_of_highest, _latest_clean_event_ts
- hermes_cli/main.py: _build_provider_choices, cmd_portal
  (portal subcommand is wired via portal_cli.add_parser, not this wrapper)
- hermes_cli/model_switch.py: CustomAutoResult (orphaned by the switch_model() extraction)
- hermes_cli/models.py: format_model_pricing_table, fetch_nous_account_tier
- hermes_cli/portal_cli.py: _nous_portal_base_url
- hermes_cli/proxy/server.py: handle_models_fallback (defined but never registered on the router)
- tools/computer_use/cua_backend.py: _parse_element, _is_arm_mac
- tools/file_operations.py: _get_safe_write_root (prod uses the imported
  agent.file_safety.get_safe_write_root directly)
- tools/skills_tool.py: _load_category_description

Also dropped two imports left unused by the removals:
- tools/file_operations.py: get_safe_write_root alias
- tools/computer_use/cua_backend.py: import platform

Pure deletion: -551 LOC. No behavior change. Test files covering the edited
modules pass (640/640); the broader suite's pre-existing/env-dependent
failures reproduce unchanged on origin/main.

hermes_cli/debug.py

@@ -256,17 +256,6 @@ def _schedule_auto_delete(urls: list[str], delay_seconds: int = _AUTO_DELETE_SEC
     policy handles cleanup.
     """
     _record_pending(urls, delay_seconds=delay_seconds)
-
-
-def _delete_hint(url: str) -> str:
-    """Return a one-liner delete command for the given paste URL."""
-    paste_id = _extract_paste_id(url)
-    if paste_id:
-        return f"hermes debug delete {url}"
-    # dpaste.com — no API delete, expires on its own.
-    return "(auto-expires per dpaste.com policy)"
-
-
 def _upload_paste_rs(content: str) -> str:
     """Upload to paste.rs.  Returns the paste URL.