feat: DailyPaper SSE streaming, LLM filter, email push, persisted config

[jerry609]

Summary

The /api/research/paperscool/daily endpoint times out (502 after 5 min) when LLM analysis or Judge is enabled because the frontend proxy buffers the entire response. This issue tracks converting the DailyPaper pipeline to SSE streaming with real-time progress, adding post-judge paper filtering, email push notifications, and persisting all config settings.

Changes

Backend

• SSE streaming for /daily: When LLM or Judge is enabled, the endpoint returns text/event-stream with per-phase progress events (search → build → LLM → judge → filter → save → notify → result). Fast path (no LLM/Judge) remains sync JSON.
• Post-judge paper filtering: After judge scoring, papers with recommendation "skip" or "skim" are removed. Only "must_read" and "worth_reading" papers are kept. Complete judge logs are preserved in the filter.log field.
• Email push: New notify_email_to field on DailyPaperRequest allows the frontend to pass recipient email directly, overriding env config.
• Judge cap raised: judge_max_items_per_query limit raised from 20 to 200.

Frontend

• SSE-aware proxy: daily/route.ts detects upstream content-type and pipes SSE streams through without buffering.
• StreamProgressCard: Real-time progress display showing current phase, progress bar, elapsed time, and detailed log (including per-paper judge scores and filter decisions).
• runDailyPaperStream(): Replaces sync runDailyPaper() — reads SSE events and progressively updates the store (papers appear one-by-one as judge scores arrive).
• Persisted config: All feature toggles (LLM, Judge, sources, etc.) are persisted in zustand store — no more re-checking on page refresh. All features default to enabled.
• Email notification UI: Email address input + enable checkbox in settings sheet.

Bug fixes

• Fixed @dataclass inheritance in errors.py (subclass defaults not applied)
• Fixed ensure_execution_result treating raw dicts as result dicts in executable.py

Testing

• 215 unit tests pass, 0 failures
• 3 new end-to-end tests for the SSE pipeline (filter, full pipeline, sync fallback)
• Next.js build passes