Weekly log as guided interview

[sarthakagrawal927]

Summary

The weekly log is now a short guided interview instead of a single prompt:

• Opens with one question, then asks the next most relevant question each turn until the person taps "I'm done — keep this week".
• Kept answers stay visible as muted Q&A blocks; on save they compose into the week's entry (promptText keeps the opening question).
• classifier.dev picks each turn's family from categorical signals: asked families are excluded from later picks, each turn is seeded so consecutive picks don't collapse, and detectThemes() runs on-device — answer prose never leaves the app. Fallback rotation covers service failure.
• "A different question" skips the current family too, so cycling actually changes topic.
• Existing entries render in plain edit mode ("Update this week") — no re-interviewing history.
• NudgeSignals gains detectedThemes / askedFamilies / turn; the API route validates all three against the family taxonomy.
• Docs (PRODUCT.md, overview) describe the interview loop.

Test plan

• pnpm quality — all gates green
• Unit tests: theme detection, turn-aware context, family exclusion
• E2E: full interview flow in local mode (answer → next question → I'm done → composed entry persists across reload); axe sweep clean
• Auth-mode save/edit still green
• Post-merge deploy via workflow

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