Introduce automatic healing for stale PDF parse states in API routes. Add
`isDocumentParseStateStale` utility and use a shared `COMPUTE_OP_STALE_MS`
environment variable (with config getter) to control the stale window for both
worker op replacement and app-side parse-state healing. Update documentation and
environment variable references to reflect new config.
Enables automatic marking of stuck parses as failed, improving reliability and
retry behavior in distributed compute environments.
Introduce detailed progress reporting for PDF layout parsing, exposing phase and page-level updates to clients. Replace legacy parseStatus with a structured parseState field in the database schema, updating all relevant backend and API logic. Add SSE endpoint for real-time parse progress updates. Update client hooks and UI to reflect granular progress and improve user feedback during document parsing. Includes migration scripts and new parse-state utility module.
