Settings web UI with live status and logs (native wizard for first launch only)

[rowkav09]

Rowan (23 Sept): he wants a web UI for the app's settings instead of the native wizard. The native wizard stays for install/first launch only, and the web UI should let him see logs and similar diagnostics.

Plan:

• Served by the running app on loopback only (127.0.0.1, random port, per-session token in the URL, same origin and CSRF guards as setup). Opened from the tray with "Open settings".
• Pages: Status (provider connection, last poll, what's playing, Discord connection, card URL, version and update state), Settings (servers, Discord idle behaviour, privacy, start with Windows, updates), Logs (live tail of the app log with level filter and a copy-diagnostics button that redacts tokens, URLs and usernames).
• Changes apply live where safe; otherwise the app restarts itself.
• Replaces tray "Run setup again" for day-to-day changes. Multi-server management lives here (Multiple media servers in one install #252).

[rowkav09]

Rowan (23 Sept): the current UI is "horrid". Proper settings are needed, using drpp's settings UI as the design starting point.

[rowkav09]

Sub-issues: #272 (Discord section), #290 (Hosted card section).