Merge branch 'main' into garrytan/team-supabase-store

Brings in 48 commits from main (v0.15.7–v0.15.16): deterministic slugs,
TabSession refactor, pair-agent tunnel fix, content security layers,
community security wave, team-friendly install, interactive snapshots.

Conflict resolution:
- .gitignore: merged both sides (kept .factory/ + added .kiro/.opencode/
  .slate/.cursor/.openclaw/ from main)
- open-gstack-browser/SKILL.md: accepted main (renamed from .factory/)
- setup-team-sync/SKILL.md: regenerated via gen:skill-docs
- test/fixtures/golden/*: updated golden baselines for ship SKILL.md
- codex-ship-SKILL.md: accepted main (renamed from .factory/)
- package.json version: synced to VERSION (0.15.16.0)
- bin/gstack-uninstall: check settings file exists before claiming
  SessionStart hook removal (fixes false positive on clean systems)

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

supabase/migrations/003_installations_upsert_policy.sql

@@ -0,0 +1,25 @@
+-- 003_installations_upsert_policy.sql
+-- Re-add a scoped UPDATE policy for installations so the telemetry-ingest
+-- edge function can upsert (update last_seen) using the caller's anon key
+-- instead of the service role key.
+--
+-- Migration 002 dropped the overly broad "anon_update_last_seen" policy
+-- (which allowed UPDATE on ALL columns). This replacement uses:
+--   1. An RLS policy to allow UPDATE (required for any row access)
+--   2. Column-level GRANT to restrict anon to only the tracking columns
+--      the edge function actually writes (last_seen, gstack_version, os)
+--
+-- This means anon callers cannot UPDATE first_seen or installation_id,
+-- closing the residual risk from the broad RLS-only approach.
+
+-- RLS policy: allow UPDATE on rows (required for PostgREST/upsert)
+CREATE POLICY "anon_update_tracking" ON installations
+  FOR UPDATE
+  USING (true)
+  WITH CHECK (true);
+
+-- Column-level restriction: anon can only UPDATE these three columns.
+-- PostgreSQL GRANT UPDATE (col, ...) is enforced at the query level —
+-- any UPDATE touching other columns will be rejected with a permission error.
+REVOKE UPDATE ON installations FROM anon;
+GRANT UPDATE (last_seen, gstack_version, os) ON installations TO anon;