feat(web): add Serper search provider plugin

[ViezeVingertjes]

What does this PR do?

Adds a bundled serper web provider plugin so Hermes can use Serper.dev as a search backend in the existing plugin-based web provider architecture.

The provider is search-only (matching Serper’s role here) and normalizes Serper API responses into Hermes’ existing web result contract.

Type of Change

• 🚀 New feature (non-breaking addition)

Changes Made

• Added new bundled web plugin:
  • plugins/web/serper/plugin.yaml
  • plugins/web/serper/__init__.py
  • plugins/web/serper/provider.py
• Provider behavior:
  • backend name: serper
  • availability gated by SERPER_API_KEY
  • search endpoint call to POST {SERPER_BASE_URL|https://google.serper.dev}/search
  • request payload includes q and num
  • response normalization from organic[] → {title,url,description,position}
  • search-only capabilities (supports_search=True, supports_extract=False)
• Wired backend selection/availability in web tools:
  • _get_backend() accepts and can auto-detect serper
  • _is_backend_available("serper")
  • check_web_api_key() recognizes configured/available serper
• Updated registry/docs/comments to include serper in provider lists and legacy preference order.
• Added/updated tests:
  • new tests/tools/test_web_providers_serper.py
  • updated plugin discovery/capability coverage in tests/plugins/web/test_web_search_provider_plugins.py
  • updated shared provider registration in tests/tools/conftest.py
  • updated config/backend selection coverage in tests/tools/test_web_tools_config.py

How to Test

# Focused provider + wiring coverage
scripts/run_tests.sh \
  tests/tools/test_web_providers_serper.py \
  tests/plugins/web/test_web_search_provider_plugins.py \
  tests/tools/test_web_tools_config.py \
  tests/tools/test_web_providers.py

Expected result:

• 4 files, 130 tests passed, 0 failed.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run tests relevant to this change and they pass
• I've added tests for my changes
• I've tested on my platform: Linux

Documentation & Housekeeping

• I've updated relevant documentation/comments where provider lists are enumerated
• No new user-facing config keys in cli-config.yaml.example required (uses existing web.backend)
• No architecture/workflow doc changes required in CONTRIBUTING.md / AGENTS.md
• I've considered cross-platform impact (network/env-var based provider, no OS-specific paths)

[haorannlp]

why closed?

[ViezeVingertjes]

why closed?

Cleaned up the fork on my end; so i think that auto-closed it (would assume so).