Complete message documentation (qqq.json) for all translatable strings

[siebrand]

Rewrites translations/qqq.json to document all 835 translatable strings in en.json, based on actual source code usage.

Each entry tells translators:

• What the string is (button label, dialog title, error message, status indicator, context menu item, placeholder, etc.)
• Where it appears in the UI
• What parameters ($1, $2, etc.) contain

Additionally:

• Expands all abbreviations (WS, SDP, RTC, 2FA, TOTP, DM, NSFW, TOS, VAD, TTS)
• Notes Markdown usage where applicable
• Documents {{PLURAL}} parameters
• Uses {{doc-important|...}} for strings needing special handling (silly phrases, language name, webhook defaults, welcome messages)
• Explains non-obvious terminology (soundboard, deafen, hoisting)
• Answers open translator questions from translatewiki.net