[pi-extension] Reflection Engine Improvements

[codenamekt]

Overview

Improve the reliability and quality of the session reflection feature.

Issues to Address

• JSON parsing fails silently — extract JSON robustly (try multiple patterns, fallback to text extraction, log failures)
• Hardcoded 4000 char slice — use token-aware truncation (~4 chars/token approximation)
• No structured extraction metadata — extract richer info: project names, dates, decisions, follow-ups into memory metadata
• No reflection model fallback — if primary model unavailable, try claude-haiku-4-20250514 as fallback before giving up
• Reflection results not surfaced — show "N facts extracted, M stored" with option to review before saving (opt-in)

Acceptance Criteria

• JSON parse failures logged with fallback text extraction
• Token-aware truncation (approximate 4 chars/token)
• Memory metadata includes extracted categories (project, decision, follow-up, etc.)
• Model fallback chain: configured model → claude-haiku-4 → skip with warning
• Optional review mode: show extracted facts before storing