Document HTTP interfaces and end-user conversion workflows

[DenWin]

Parent: #24. Coordinate with #9-#15 and #19-#23.

Deliverables

HTTP interface reference

For each supported route/interface document:

• method and path
• authentication requirement
• request parameters/body
• successful response or redirect
• validation errors and status codes
• ownership/security rules
• side effects
• examples safe for copy/paste

Cover setup, registration, login/logout, root/job creation, upload, target discovery, conversion submission, progress, results, history, download/archive, deletion, account, and health.

Clearly mark browser-internal endpoints versus interfaces intended for external automation. Do not promise a public API unless it is intentionally supported.

User workflows

• first-run setup
• login and returning session
• single and multi-file conversion
• choosing targets/converters
• batch and per-file settings
• filename templates
• progress, retry, results, history, downloads, and deletion
• error recovery and unsupported conversions
• accessibility/keyboard guidance where appropriate

Acceptance criteria

• Examples are validated against the application.
• Authentication and destructive side effects are prominent.
• Error cases are documented, not only happy paths.
• Planned Epic: Redesign authentication and multi-file conversion workflow #9 behavior is marked as planned until implemented.
• Route documentation has a maintenance owner or generation/check strategy.