fix(knowledge): stabilize mutation timestamps

[akoita]

Outcome

Keep candidate-knowledge application timestamps nondecreasing when the wall clock moves backward, preventing valid follow-up mutations from tripping storage anti-rollback validation.

Refs #389. #389 remains open until post-merge validation confirms the main revision.

Evidence

A deterministic one-hour backward-clock case reproduced the previously captured StorageValidationError: checkedAt preceded the persisted refresh observation. The regression now passes through a service-local monotonic timestamp source.

Scope

• add a focused monotonic timestamp helper
• wire candidate-knowledge service-generated timestamps through it
• preserve invalid timestamp passthrough and storage validation
• cover helper behavior and the real file-refresh boundary
• update the v0.9 roadmap

Validation

• focused application + desktop host: 175/175 tests
• pnpm validate: 105/105 Vitest files, 1,596/1,596 tests, 54/54 release/security tests
• architecture hotspot: packages/application/src/knowledge-base.ts remains at 6,168 lines

Limitations

This fixes the proven within-service wall-clock regression mechanism. It does not weaken storage anti-rollback checks or claim that every earlier intermittent mutation failure had the same cause.