test: add comprehensive tests for Phase 1 tasks 1.10-1.18

- Parser tests: scope metadata parsing (top-level, nested, backward compat,
  invalid trigger/globs rejection, metadata propagation to rules)
- Config tests: v0.1/v0.2 version handling, global field, version validation
- Schema tests: validateScopeMetadata, isValidTrigger, VALID_CONFIG_VERSIONS
- Compile integration tests: DirectoryBridge multi-file output, MarkerBridge
  output, mixed bridges, stale file cleanup, legacy migration, dry-run mode
- Explain tests: multi-file mode label, per-scope file listing
- E2E tests: multi-file compile, dry-run, explain multi-file paths
- Output tests: updated mode label assertion

Author: gpolanco