feat(tools): add web_search and web_fetch tools

[devproje]

What this changes

compute_use (modules/browser) already covers browser automation + screenshot capture. This adds two more read-only tools: web_search (Brave, Tavily, or Ollama Search — whichever backend is selected) and web_fetch (a direct, SSRF-guarded GET, or Tavily's extract endpoint when Tavily is the selected backend).

Backend configuration is a new web_providers table managed via mininaru webprovider add/list/show/set/primary/remove. It follows the single-selection shape agents.selected uses (one row selected at a time via a unique partial index), not the active-column shape providers once had and later dropped in 0007_agent_selected_provider_active_removal.sql — reusing the pattern the project kept, not the one it abandoned. api_key is encrypted at rest the same way providers.api_key already is.

modules/web_search/modules/web_fetch take a WebBackendLookup closure from core/tools.go rather than importing core directly, since core already imports them and a direct import would cycle.

Also renames a batch of pre-existing multi-word filenames to snake_case for consistency with the new files (core/agentspawn.go → agent_spawn.go, util/apikey.go → api_key.go, and others), and fixes the stale filenames docs/ARCHITECTURE.md referenced.

How it was verified

• make test-race passes
• New behaviour has a test, or there is nothing to test

Added core/web_provider_test.go (CRUD + auto-select-first + WebProviderSelect/WebProviderSelected, mirroring core/agent_test.go's style), modules/web_fetch/web_fetch_test.go (the bogon/SSRF guard actually rejects loopback/private/link-local addresses, including against a real httptest.Server on 127.0.0.1), and modules/web_search/web_search_test.go (arg validation, backend dispatch, result formatting).

Checklist

• Follows docs/CONVENTION.md: no comments, no :=, one var block per function in first-use order with err last, callees before callers, and main unconditionally last
• New .go files carry the two-line SPDX header
• Documentation updated if behaviour a user can see has changed (docs/ARCHITECTURE.md)
• My contribution is licensed GPL-3.0-only, matching the project