REST API for snippets

[byteofhoney]

Goal:

Expose snippet data as JSON over a proper API, separate from HTML routes.

User story:

As a developer, I want a REST API so that I can build tools (like a browser extension) on top of StashSnip.

Tasks:

• New blueprint (e.g. app/api.py) mounted under /api
• Endpoints: GET /api/snippets, GET /api/snippets/
• Reuse existing DB/model logic instead of duplicating query code
• Decide and document auth scope for this issue (open API to start is fine)

Acceptance Criteria:

• Both endpoints return correct JSON with proper status codes (200, 404)
• No duplicate business logic between HTML routes and API routes
• Documented (even briefly) in the README or a docs file