feat(web): add Brave Search (free tier) and DDGS search providers

Both implement WebSearchProvider via tools/web_providers/ — matching the
existing SearXNG pattern (PR #5c906d702). Search-only; pair with any
extract provider via web.extract_backend.

- tools/web_providers/brave_free.py — Brave Search API (free tier, 2k
  queries/mo). Uses BRAVE_SEARCH_API_KEY as X-Subscription-Token.
- tools/web_providers/ddgs.py — DuckDuckGo via the ddgs Python package.
  No API key; gated on package importability.
- tools/web_tools.py: both backends added to _get_backend() config list
  and auto-detect chain (trails paid providers), _is_backend_available,
  web_search_tool dispatch, web_extract_tool + web_crawl_tool search-only
  refusals, check_web_api_key, and the __main__ diagnostic. Introduces
  _ddgs_package_importable() helper so tests can monkeypatch a single
  symbol for the ddgs availability check.
- hermes_cli/tools_config.py: picker entries for both providers; ddgs
  gets a post_setup handler that runs `pip install ddgs`.
- hermes_cli/config.py: BRAVE_SEARCH_API_KEY in OPTIONAL_ENV_VARS.
- scripts/release.py: AUTHOR_MAP entry for @Abd0r.
- tests: 14 new tests (brave-free) + 15 new tests (ddgs) covering
  provider unit behavior, backend wiring, and search-only refusals.

Salvages the brave-free + ddgs portion of PR #19796. Not included: the
in-line helpers in web_tools.py (replaced with provider modules to match
the shipped architecture), the lynx-based extract path (these backends
should refuse extract with a clear error — users pair with a real
extract provider), and scripts/start-llama-server.sh (unrelated).

Co-authored-by: Abd0r <223003280+Abd0r@users.noreply.github.com>

hermes_cli/config.py

@@ -1864,6 +1864,14 @@ OPTIONAL_ENV_VARS = {
         "password": False,
         "category": "tool",
     },
+    "BRAVE_SEARCH_API_KEY": {
+        "description": "Brave Search API subscription token (free tier: 2,000 queries/mo)",
+        "prompt": "Brave Search subscription token",
+        "url": "https://brave.com/search/api/",
+        "tools": ["web_search"],
+        "password": True,
+        "category": "tool",
+    },
     "BROWSERBASE_API_KEY": {
         "description": "Browserbase API key for cloud browser (optional — local browser works without this)",
         "prompt": "Browserbase API key",