"UI overhaul with dark/light palettes, granular document removal, and search scoring fix"

v0.8.3 changelog:

• Dark & light mode palettes redesigned — CSS variable theming with data-theme switching, five cycling tag colors, gradient action buttons, unified score badges
• 4-option trash modal — remove from index, remove & blacklist, remove & delete from disk (double-confirm), cancel. New /api/delete?mode= parameter (backward-compatible default: db_only)
• Search scoring fixed ("both" mode) — semantic floor at 0.30, max-based scoring replaces weighted average that was capping keyword hits at 0.3
• scan embeds by default — new installs get semantic search working immediately; --no-embed flag for opt-out
• Security hardening — CSRF on /api/download and /api/synopsis, CORS restriction in remote mode, exception leak suppression
• Remote card cleanup — file path hidden in remote mode