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/main.py

@@ -6158,15 +6158,6 @@ def cmd_webhook(args):
     from hermes_cli.webhook import webhook_command
 
     webhook_command(args)
-
-
-def cmd_portal(args):
-    """Nous Portal status and Tool Gateway routing surface."""
-    from hermes_cli.portal_cli import portal_command
-
-    return portal_command(args)
-
-
 def cmd_slack(args):
     """Slack integration helpers.
 
@@ -10975,24 +10966,6 @@ def cmd_logs(args):
         since=getattr(args, "since", None),
         component=getattr(args, "component", None),
     )
-
-
-def _build_provider_choices() -> list[str]:
-    """Build the --provider choices list from CANONICAL_PROVIDERS + 'auto'."""
-    try:
-        from hermes_cli.models import CANONICAL_PROVIDERS as _cp
-        return ["auto"] + [p.slug for p in _cp]
-    except Exception:
-        # Fallback: static list guarantees the CLI always works
-        return [
-            "auto", "openrouter", "nous", "openai-codex", "xai-oauth", "copilot-acp", "copilot",
-            "anthropic", "gemini", "google-gemini-cli", "xai", "bedrock", "azure-foundry",
-            "ollama-cloud", "huggingface", "zai", "kimi-coding", "kimi-coding-cn",
-            "stepfun", "minimax", "minimax-cn", "kilocode", "novita", "xiaomi", "arcee",
-            "nvidia", "deepseek", "alibaba", "qwen-oauth", "opencode-zen", "opencode-go",
-        ]
-
-
 # Top-level subcommands that argparse knows about WITHOUT running plugin
 # discovery.  Used to short-circuit eager plugin imports (which can take
 # 500ms+ pulling in google.cloud.pubsub_v1, aiohttp, grpc, etc.) when the