feat(web): saved queries UI, file upload on ingest, playground hybrid/rerank

[erichare]

Summary

UI catch-up for the phase-2b backend tail. Brings the web app in line with features that have already shipped server-side: saved queries, hybrid + rerank toggles, and proper file uploads.

• Saved queries in each catalog row: list, create, delete, one-click replay. New useSavedQueries hooks + SavedQueriesSection component, rendered inside the expanded catalog row under the document list. Talks to the existing /catalogs/{c}/queries + /queries/{q}/run routes.
• Ingest dialog now has a drag-and-drop + click-to-browse file picker for text-ish formats (.txt, .md, .json, .csv, .yaml, …). Reads the file into the textarea and auto-fills sourceFilename. 5 MB cap, clear toast errors on unsupported types or oversize files.
• Playground QueryForm Hybrid + Rerank toggles wired to the runtime flags. Validation blocks hybrid/rerank on the Vector tab (they require a text query). Descriptions surface whether the bound store has lexical/reranking enabled.

No backend changes — all routes and schemas already exist.

Test plan

• pnpm typecheck clean (passes locally)
• pnpm lint clean (passes locally)
• pnpm --filter ai-workbench-web build clean (passes locally)
• Manual: create a saved query from the catalog row, verify it persists after reload, run it, delete it
• Manual: drop a .md file onto the ingest dialog, confirm textarea fills and filename auto-populates
• Manual: toggle Hybrid on a lexical-enabled store, verify results differ from pure vector
• Manual: toggle Rerank on a reranking-enabled store, verify hit order changes

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