feat: add web inspection interface

[gokul-debugger]

Summary

• serve a lightweight browser interface from the FastAPI root route
• support issue reference and optional actor input with loading, success, and error states
• render reports with safe DOM APIs and accessible live status updates
• serialize canonical issue URLs and document the browser workflow
• keep /docs available and avoid accepting or storing tokens in the page

Testing

• python -m pytest (52 passed)
• ruff check .
• ruff format --check .
• mypy src tests
• git diff --check
• manually verified successful and invalid-reference browser flows

Closes #2