Public API docs and landing-message polish
xpenser added public API documentation and polished landing messaging so developers can inspect the finance API before integrating.

The public site gained API documentation that makes xpenser more useful as both an app and a developer-facing finance system.
This release came from PR #52 and is now part of the xpenser release archive. It gives people evaluating an open-source expense tracker a clearer view of how the product has improved over time.
What changed
- Added public Swagger/OpenAPI documentation.
- Polished landing messaging for API and MCP use cases.
- Verified the public API contract path in preview.
Why it matters
Developers evaluating a finance app need to see its API shape quickly. Public docs reduce setup friction and support integrations.
Where it fits
This release strengthens the personal finance API and MCP path for xpenser.
For a broader product overview, start with the xpenser home page. Developers can also explore the personal finance API and MCP tools, while self-hosters can review the self-hosted personal finance tracker page.