Address review: warn on ignored provider, clarify cache comment, drop bot analysis churn

- Hosted modes pin OpenRouter because the free/license tiers run on CodeBoarding's
  OpenRouter account; to use another provider you set llm_api_key (BYO-key mode,
  which is unchanged). Added a `::warning::` when llm_provider is non-OpenRouter
  but no key is given, so a provider choice isn't silently ignored.
- Clarified the cache-key comment: the mode discriminator only matters between
  free-tier (forced Gemini) and a BYO *OpenRouter* key with no model pinned — those
  would otherwise share a cache key but produce different base analyses.
- Reverted .codeboarding/analysis.json + health_report.json to origin/main: a
  codeboarding[bot] commit (dogfooding during testing) had been rebased into this
  branch and was polluting the PR diff. The repo keeps its baseline; the PR no
  longer churns it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Svilen-Stefanov