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>

pyproject.toml

@@ -27,6 +27,7 @@ dependencies = [
   "prompt_toolkit",
   # Tools
   "firecrawl-py",
+  "parallel-web>=0.4.2",
   "fal-client",
   # Text-to-speech (Edge TTS is free, no API key needed)
   "edge-tts",