feat: unified gstack eval CLI with list, compare, push, cache, cost

- lib/cli-eval.ts: routes to list/compare/summary/push/cost/cache/watch
  subcommands. Ports logic from 4 separate scripts into unified entry.
  Adds ANSI color for TTY (respects NO_COLOR), --limit flag for list.
- bin/gstack-eval: bash wrapper matching bin/gstack-sync pattern
- package.json: eval:* scripts now point to lib/cli-eval.ts
- supabase/migrations/004_eval_costs.sql: per-model cost tracking + RLS
- docs/eval-result-format.md: public format spec for any language
- test/lib-eval-cli.test.ts: integration tests (spawn CLI subprocess)
  including 3 push failure modes (file-not-found, invalid schema,
  sync unavailable)

215 tests passing across 13 files.

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

package.json

@@ -18,10 +18,10 @@
     "skill:check": "bun run scripts/skill-check.ts",
     "dev:skill": "bun run scripts/dev-skill.ts",
     "start": "bun run browse/src/server.ts",
-    "eval:list": "bun run scripts/eval-list.ts",
-    "eval:compare": "bun run scripts/eval-compare.ts",
-    "eval:summary": "bun run scripts/eval-summary.ts",
-    "eval:watch": "bun run scripts/eval-watch.ts"
+    "eval:list": "bun run lib/cli-eval.ts list",
+    "eval:compare": "bun run lib/cli-eval.ts compare",
+    "eval:summary": "bun run lib/cli-eval.ts summary",
+    "eval:watch": "bun run lib/cli-eval.ts watch"
   },
   "dependencies": {
     "playwright": "^1.58.2",