Docs indexing fixes

[RomneyDa]

• Only index docs if docs context provider is present
• Only index docs if disableIndexing is true
• Abort indexing if indexing is disabled mid-index
• Add embeddingProviderId column to SQLite DB (the migration is simply full table deletion which is fine since that's what already happens on an embedding provider change). This way, docs are only reindexed on profile change if it's a new embedding provider embed id
• Add a "add @docs context provider" prompt link to More page if @docs is not in config
• Fix docs indexing peeks logic that wasn't only displaying docs found in config
• Fix various small logic bugs in docs service

[netlify]

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