Task: Add a new phase to an existing implementation plan

An implementation plan already exists at .context/plans/plan-blog-platform/. The plan currently has two phases:

• phases/phase-01-workspace-bootstrap/ (3 tasks — all complete)
• phases/phase-02-data-model/ (4 tasks — all complete)

You need to extend this plan with a new phase covering the REST API layer. The API layer must implement:

1. GET /posts — list all posts (paginated, 10 per page)
2. POST /posts — create a new post (title, body, author required)
3. GET /posts/:id — get a single post by ID
4. PUT /posts/:id — update title/body of a post
5. DELETE /posts/:id — delete a post (soft delete — set deleted_at)
6. GET /health — health check returning {"status":"ok"}

Use Express.js. All handlers must be in separate files under src/api/.

Add this as phase 3 to the existing plan.

Additive-only constraint

The following files already exist and are read-only — they MUST NOT be modified, renamed, or deleted under any circumstances:

• phases/phase-01-workspace-bootstrap/ and all files within it
• phases/phase-02-data-model/ and all files within it

The root README.md may have a new phase-03 entry appended to its phase listing. No other edits to the root README are permitted.

Only new files may be created: the phase-03 directory, its README, and its task files.