[githubflyideas]

Adds Midnight as the fifth theme in the picker (deep navy #0b1020, cyan #22d3ee accent / inbound, violet #a78bfa outbound, frosted-glass cards).

UI files only: theme.js, app.css, app.js, i18n/*.json, CHANGELOG. No Go, collector, decoder, DB, API or licensing changes.

• theme.js: 'midnight' appended to THEMES; dark-logo variant via a DARK set (black, midnight); exposes t66Theme.isDark().
• app.css: new :root[data-theme=midnight] block defining every variable the default block defines; map ramp runs dark to bright (brighter = more traffic). Midnight-only scoped styles: frosted-glass panels/topbar (solid --surface fallback when backdrop-filter is unsupported), soft glow under area fills, cyan-to-violet share bars, gradient/glow active sidebar item.
• app.js: THEME_PAL.midnight='pp'; the black-only checks (flow-line lightening of the two darkest shades, logo preview) now use isDarkTheme() (true for black and midnight; black unchanged). Logo upload label uses var(--on-accent) instead of #fff (resolves to #fff in all existing themes; dark ink on cyan in Midnight).
• i18n: theme.midnight in all 15 languages.

Existing four themes: screenshots against main differ only in live elements (clock / sponsor rotation).