[Feature]: add Serply as a web-search provider

[googio]

Problem or Motivation

OpenMAIC's web-search layer currently offers Tavily, Exa, Bocha, Brave, Baidu, SearXNG, MiniMax, Claude and Doubao. Users who already hold a Serply API key (a Google SERP API at https://serply.io) have no way to plug it into classroom generation without standing up a SearXNG instance or buying a second search subscription. The provider registry in lib/web-search/constants.ts and the adapter switch in lib/web-search/index.ts are designed for exactly this kind of addition, and the recent Exa provider (#1342) shows the accepted shape.

Disclosure: I am affiliated with Serply. This is a bring-your-own-key integration; nothing in OpenMAIC changes for users who do not configure it.

Proposed Solution

Add serply as a new API-key web-search provider, mirroring the Exa integration end to end:

• lib/web-search/serply.ts: searchWithSerply calling GET https://api.serply.io/v1/search/?q=...&num=N with the X-Api-Key header via proxyFetch, mapping results[] (title, link, description) to WebSearchSource entries and dropping results without a URL.
• Registry entry in WEB_SEARCH_PROVIDERS, 'serply' in WebSearchProviderId, dispatch case in searchWeb, env key name in the web-search route, SERPLY_API_KEY / SERPLY_BASE_URL / SERPLY_ENABLED in the server provider config, official base URL allowlist entry, default client settings + migration in lib/store/settings.ts.
• settings.providerNames.serply in all 12 locales, .env.example, configuration.mdx + supported-models.mdx in all 6 doc locales, and skills/openmaic/references/provider-keys.md.
• Vitest coverage: adapter unit tests, dispatch, route, server config, constants, and the provider-neutrality guard debt table.

Acceptance Criteria

• A user can pick "Serply" under Settings > Web Search, enter an API key, and classroom generation uses it for web research.
• A self-hoster can configure it server-side with SERPLY_API_KEY (plus optional SERPLY_BASE_URL, SERPLY_ENABLED=false) and the client shows it as server-managed.
• The system returns a clear error naming SERPLY_API_KEY when the provider is selected without credentials.
• Existing providers continue to work; pnpm format, pnpm lint, npx tsc --noEmit and pnpm test stay green.

Alternatives Considered

• Pointing users at SearXNG with a Serply engine: requires self-hosting a second service and loses the key-based server-managed flow OpenMAIC already supports.
• A generic "custom HTTP search" provider: larger design change, and the neutrality guard intentionally keeps vendor knowledge inside per-provider adapters.

Area

Model / provider integration

Additional Context

I have the implementation ready and can open the PR right after this issue is acknowledged. It will be marked AI-assisted per CONTRIBUTING and includes Settings screenshots.

[googio]

I would like to take this one. Implementation is in progress on a feat/serply-search branch; PR to follow shortly.