[Backend] Expose Task Pack refinement cache status

[drag1web]

Problem

The Task Pack refinement pipeline already tracks whether generation came from the refinement cache, but that status is not exposed consistently through the stored/public Task Pack contract.

Current repository state:

• generateReliableTaskPack(...) returns cached: boolean;
• generation diagnostics also contain cached;
• the renderer Task Pack type already includes optional generationCached?: boolean;
• the storage Task Pack contract does not currently persist/expose generationCached;
• server/src/routes/taskPacks.ts stores generation metadata but does not pass generation.cached into the stored Task Pack record.

Goal

Expose whether the Task Pack refinement was served from cache as a public boolean field without duplicating cache-state logic.

Expected behavior

When a Task Pack is generated, the resulting stored/API Task Pack record should expose:

generationCached: boolean

The value must come from the existing generateReliableTaskPack(...).cached result.

Scope

Likely areas to inspect:

• server/src/routes/taskPacks.ts
• server/src/storage/types.ts
• SQLite/PostgreSQL Task Pack persistence and mapping
• relevant storage migrations if persistence requires a new column
• renderer/shared Task Pack contract
• focused generation/storage smoke coverage

Keep the change focused. Do not create a second cache-status source of truth.

Acceptance criteria

• Task Pack generation exposes generationCached as a boolean.
• Cache hits produce generationCached: true.
• Non-cached/template/fallback generation produces generationCached: false.
• The value is sourced from existing generation cache diagnostics/result state.
• Persistence and API reads remain consistent across supported storage adapters.
• Existing Task Pack generation behavior remains unchanged apart from exposing the metadata.
• Relevant build and focused smoke checks pass.

Notes

This issue was originally created from a generated ContextForge Task Pack. The large generated prompt and diagnostic dump were removed to keep the public backlog focused and reviewable.