feat(web): add Parallel as alternative web search/extract backend (#1696)

* feat(web): add Parallel as alternative web search/extract backend

Adds Parallel (parallel.ai) as a drop-in alternative to Firecrawl for
web_search and web_extract tools using the official parallel-web SDK.

- Backend selection via WEB_SEARCH_BACKEND env var (auto/parallel/firecrawl)
- Auto mode prefers Firecrawl when both keys present; Parallel when sole backend
- web_crawl remains Firecrawl-only with clear error when unavailable
- Lazy SDK imports, interrupt support, singleton clients
- 16 new unit tests for backend selection and client config

Co-authored-by: s-jag <s-jag@users.noreply.github.com>

* fix: add PARALLEL_API_KEY to config registry and fix web_crawl policy tests

Follow-up for Parallel backend integration:
- Add PARALLEL_API_KEY to OPTIONAL_ENV_VARS (hermes doctor, env blocklist)
- Add to set_config_value api_keys list (hermes config set)
- Add to doctor keys display
- Fix 2 web_crawl policy tests that didn't set FIRECRAWL_API_KEY
  (needed now that web_crawl has a Firecrawl availability guard)

* refactor: explicit backend selection via hermes tools, not auto-detect

Replace the auto-detect backend selection with explicit user choice:
- hermes tools saves WEB_SEARCH_BACKEND to .env when user picks a provider
- _get_backend() reads the explicit choice first
- Fallback only for manual/legacy config (uses whichever key is present)
- _is_provider_active() shows [active] for the selected web backend
- Updated tests, docs, and .env.example to remove 'auto' mode language

* refactor: use config.yaml for web backend, not env var

Match the TTS/browser pattern — web.backend is stored in config.yaml
(set by hermes tools), not as a WEB_SEARCH_BACKEND env var.

- _load_web_config() reads web: section from config.yaml
- _get_backend() reads web.backend from config, falls back to key detection
- _configure_provider() saves to config dict (saved to config.yaml)
- _is_provider_active() reads from config dict
- Removed WEB_SEARCH_BACKEND from .env.example, set_config_value, docs
- Updated all tests to mock _load_web_config instead of env vars

---------

Co-authored-by: s-jag <s-jag@users.noreply.github.com>

AGENTS.md

@@ -44,7 +44,7 @@ hermes-agent/
 │   ├── terminal_tool.py  # Terminal orchestration
 │   ├── process_registry.py # Background process management
 │   ├── file_tools.py     # File read/write/search/patch
-│   ├── web_tools.py      # Firecrawl search/extract
+│   ├── web_tools.py      # Web search/extract (Parallel + Firecrawl)
 │   ├── browser_tool.py   # Browserbase browser automation
 │   ├── code_execution_tool.py # execute_code sandbox
 │   ├── delegate_tool.py  # Subagent delegation