refactor(tests): centralize lane definitions and add per-file isolation

- extract test lane config to scripts/test-lanes.ts (single source of truth)
- run-test-lane.mjs: per-file bun process isolation with wall timeout; --jobs N, --single-process flags
- drop hand-listed test file lists from package.json; lanes now discovered by directory
- add test:stats (stats/src) and test:scripts (scripts/**) lanes; wire both into CI
- test:fast now: test:src + launcher-unit + test:scripts + test:runtime:compat
- remove obsolete test:full, test:core, test:core:dist, test:config:dist scripts

AGENTS.md

@@ -42,7 +42,10 @@ Start here, then leave this file.
 - Config/schema/defaults: `bun run test:config`; if template/defaults changed, `bun run generate:config-example`
 - Launcher/plugin: `bun run test:launcher` or `bun run test:env`
 - Runtime-compat / dist-sensitive: `bun run test:runtime:compat`
+- Stats dashboard UI (`stats/`): `bun run test:stats`
+- Build/release scripts (`scripts/**`): `bun run test:scripts`
 - Docs-only: `bun run docs:test`, then `bun run docs:build`
+- Test lanes are directory-discovered via `scripts/test-lanes.ts`; never hand-list test files in `package.json`
 
 ## Docs Upkeep