Add a lightweight web inspection interface

[gokul-debugger]

Problem

The CLI and HTTP API are usable today, but people evaluating ContribCheck in a browser only see the generic OpenAPI documentation. A small product interface would make the readiness report easier to understand and demonstrate.

Proposed change

Add a lightweight web interface served by the existing FastAPI app that submits an issue reference to the existing /v1/inspect endpoint and presents the evidence-based report.

Acceptance criteria

• The page accepts a GitHub issue URL or owner/repository#number reference and an optional GitHub username (matching the CLI's --actor option, used to treat assignments and claims by that user as your own).
• Results clearly show the ready, caution, or blocked verdict.
• Every check displays its status, summary, and linked evidence when available.
• Next actions and operational errors (invalid reference, unknown issue, rate limit) are easy to scan.
• The interface has responsive, keyboard-accessible loading, empty, success, and error states.
• Browser code never stores or logs GitHub tokens.
• /docs remains available for API users.
• Focused tests cover the page response and its API interaction contract.
• The README includes startup instructions and one screenshot.

Scope

• Prefer a small implementation that fits the existing FastAPI application (e.g. FastAPI/Jinja2 templates served at GET /). A large frontend framework or separate build pipeline should be proposed before being introduced.
• Reuse /v1/inspect; do not duplicate analysis logic in the web layer.