feat: add enriched transcript sync — Haiku summaries, session file enrichment

Add session intelligence pipeline for team transcript sync:
- lib/transcript-sync.ts: parse history.jsonl, enrich with Claude session
  file data (tools_used, full turn count), sync marker management,
  10-concurrent push with 5-concurrent Haiku summarization
- lib/llm-summarize.ts: raw fetch() to Anthropic Messages API (no SDK dep),
  retry-after on 429, exponential backoff on 5xx, SHA-based eval-cache
- lib/sync.ts: pushTranscript() and pullTranscripts() following existing patterns
- 006_transcript_sync.sql: unique index on (team_id, session_id) for
  idempotent upsert, RLS changed from admin-only to team-wide read

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

supabase/migrations/006_transcript_sync.sql

@@ -0,0 +1,15 @@
+-- 006_transcript_sync.sql — Unique index for idempotent transcript upsert + RLS fix.
+
+-- Unique index on (team_id, session_id) for upsert via Prefer: resolution=merge-duplicates.
+-- session_id is a UUID from Claude Code — globally unique. No need for user_id in the key
+-- (which is nullable and breaks PostgreSQL unique index dedup on NULL values).
+create unique index if not exists idx_transcript_natural_key
+  on session_transcripts(team_id, session_id);
+
+-- Change transcript RLS from admin-only read to team-wide read.
+-- Matches the pattern used by eval_runs, retro_snapshots, qa_reports, ship_logs, greptile_triage.
+-- Opt-in transcript sync already requires user consent (sync_transcripts=true).
+drop policy if exists "admin_read" on session_transcripts;
+create policy "team_read" on session_transcripts for select using (
+  team_id in (select team_id from team_members where user_id = auth.uid())
+);