Treated SearXNG HTTP 200 responses with no usable sources and upstream engine failures as transient provider errors. Added a generic renderable-content guard so provider fallback continues instead of returning an invisible success.\n\nFixes #2571
- Added optional FetchImpl fields to compaction, proxy, AI, coding-agent, and mnemopi options.
- Threaded injected fetch implementations through OAuth, discovery, and search/LLM request flows.
- Removed exported hookFetch utility and its package entrypoint from utils.
- Replaced global-fetch test monkeypatching with per-test FetchImpl mocks across test suites.
- Removed export leakage by demoting many helper and const symbols to module-local scope.
- Renamed underscore-prefixed internals and cache fields, then updated related references and `satisfies never` checks.
- Deleted obsolete logic branches and helpers, including harmony-stream interruption flow and unused benchmark runtime helpers.
- Updated Biome config and manifests by broadening lint coverage and removing an unused `@napi-rs/cli` dev dependency.
- Adjusted tests and utilities to use renamed test helpers and remove redundant private test-only helpers/locals.
Add explicit Basic auth credentials for SearXNG while preserving Bearer token fallback.
Keep optional SearXNG settings out of the TUI and allow empty RFC 7617 username/password fields.
roboomp