Resolve #2288: discover factory and value event handlers

[ayden94]

Summary

Discover @OnEvent() handlers declared on singleton useFactory and useValue provider instances so event-bus discovery matches its singleton provider contract.

Linked context: Closes #2288

Changes

• Resolve singleton factory/value provider instances during event handler discovery.
• Keep request/transient factory handlers out of discovery with the existing non-singleton warning path.
• Add regression coverage for factory/value discovery and non-singleton factory exclusion.

Testing

• pnpm --filter @fluojs/event-bus... build
• pnpm exec biome check packages/event-bus/src/service.ts packages/event-bus/src/module.test.ts .changeset/calm-event-bus-discovery.md
• pnpm --filter @fluojs/event-bus test
• pnpm --filter @fluojs/event-bus typecheck
• pnpm --filter @fluojs/event-bus build
• pnpm verify:release-readiness
• GIT_MASTER=1 git diff --check

Release impact

• This PR has consumer-visible release impact and includes a changeset.
• This PR has no consumer-visible release impact.

Public export documentation

See docs/contracts/public-export-tsdoc-baseline.md for the repo-wide authoring baseline.

• Changed public exports include a source-level summary.
• Changed exported functions document matching @param / @returns tags where applicable.
• Source @example blocks and README scenario examples still play complementary roles.

Behavioral contract

See docs/contracts/behavioral-contract-policy.md for full details.

• No documented behavioral contracts were removed without migration notes.
• New behavioral contracts are documented in the affected package README.
• Intentional limitations are explicitly stated (not silently removed).
• Runtime invariants are covered by regression tests.

Platform consistency governance (SSOT)

See docs/architecture/platform-consistency-design.md and docs/contracts/release-governance.md.

• SSOT English/Korean mirror structure remains synchronized for changed governance docs.
• If platform contract docs changed, companion updates include discoverability/docs index, tooling or CI enforcement, and regression-test evidence.
• Any package README alignment/conformance claims are backed by createPlatformConformanceHarness(...) tests.