feat: add unit tests for plugin metadata resolution

[subhashkhileri]

Summary

• Add 55 unit tests covering all dynamic plugin config resolution scenarios
• Split tests into focused files under src/utils/tests/:
  • plugin-metadata.test.ts — pure utilities (extractPluginName, getNormalizedPluginMergeKey,
    disablePluginWrappers, generatePluginsFromMetadata)
  • plugin-metadata.pr.test.ts — PR mode: metadata injection, user override, OCI resolution, skip
    injection, precedence
  • plugin-metadata.nightly.test.ts — nightly detection (isNightlyJob), nightly resolution, user config
    preservation
  • plugin-metadata.fixtures.test.ts — realistic workspace fixtures (argocd, scorecard, github-events,
    topology, global-header, orchestrator) + edge cases
• Add shared test helpers (helpers.ts) for env var isolation and metadata fixture creation
• Add yarn build && yarn test to pre-commit hook so tests run locally before every commit

What's tested

• OCI resolution: ghcr.io, quay.io/rhdh, registry.access.redhat.com, shared images with aliases
  (redhat-resource-optimization pattern)
• Plugin config merging: metadata as base, user pluginConfig as override, deep merge with partial
  overrides
• Mode detection: E2E_NIGHTLY_MODE strict check (rejects "false"), JOB_NAME periodic detection,
  PR precedence over nightly
• Passthrough: local paths, npm packages with integrity, cross-workspace plugins, disabled plugins
• Edge cases: non-existent metadata dir, empty plugins, config local path with OCI metadata, extra
  fields preserved

Verified by breaking

Each critical code path was intentionally broken to confirm tests fail with clear messages:

Break	Tests failed
Never resolve OCI refs	10
Always inject metadata (nightly too)	3
Swap merge order (metadata wins over user)	3
Drop plugin fields during resolution	3
Include pluginConfig in generation	3
Hardcoded ghcr.io registry	9