fix: report line-only coverage honestly and tighten Bun test helpers

The generated HTML and Cobertura reports no longer show unmeasured
branch and function coverage as 100%. Poll and waitFor deadlines use
performance.now so frozen dates cannot make them loop forever, the
malformed-configuration test covers undefined again next to the empty
array, compose health checks honor PORT, and the migration spec lists
only what is still open.

Refs #291, #292, #293

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

compose.prod.yml

@@ -17,7 +17,7 @@ services:
                     'CMD',
                     'bun',
                     '-e',
-                    "fetch('http://localhost:4000/').then(r => process.exit(r.ok ? 0 : 1), () => process.exit(1))",
+                    "fetch('http://localhost:' + (process.env.PORT || 4000) + '/').then(r => process.exit(r.ok ? 0 : 1), () => process.exit(1))",
                 ]
             interval: 30s
             timeout: 10s