Add a Discord status text field to Settings

[rowkav09]

Settings > Discord gets a "Status text" box and a "Status shows" choice, so the header text from #1098/#1105 can be changed without editing config.json.

• Empty box = default "{artist} on {service}". The help lists the fields ({artist}, {title}, {subtitle}, {album}, {year}, {series}, {season}, {episode}, {service}) and says "{{ or }}" writes a literal brace.
• "Status shows": the status text (default), the second line, or the first line (Discord's status_display_type).
• Saved as discord.name / discord.statusDisplayType in config.json, kept across settings, server and setup rewrites, and passed to both the live and frozen Discord controllers. Left out when default, so existing configs are unchanged.
• Name is limited to 128 characters; invalid values are rejected.

Fail-first: test/discord-name-settings.test.js (round trip, wire payload from a saved config, page markup and save script). Suite 1584 pass, 0 fail.

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 4 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/setup-config.js	66.66%	4 Missing ⚠️

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