feat(design): port neuraldeep visual identity (palette + Inter + motion)

[vakovalskii]

What

Ports the neuraldeep hub-frontend visual identity onto codbash while keeping the zero-deps vanilla-JS architecture intact.

Before / after (dark theme — default)

	before 7.5.0	after
bg	`#1a1d23`	`#08090C` (deep cool black)
panel	`#2a2e37`	`#121418`
border	`#363b44`	`#2A2D33`
text	`#e4e7eb`	`#EBEDF0` (slightly cool)
muted	`#5f6571`	`#9499A5` (AA on the new bg)
brand accent	`#4ade80` (mint)	`#00FF88` (neon brand)
font	system stack	Inter (Google Fonts, falls back to system)

Light theme cooled to `#FAFBFC` bg + `#111827` fg + AA-safe deeper green `#10804A`.
Monokai theme untouched — kept as the retro third option.

What ships

Tokens (`src/frontend/styles.css`)

• All `:root` (dark) and `[data-theme="light"]` palette values replaced
• RGB-triplet aliases (`--c-accent` / `--c-bg` / `--c-panel` / `--c-border` / `--c-fg` / `--c-muted`) added — enables `rgb(var(--c-accent) / 0.12)` alpha-modulation
• Semantic accents (blue/orange/purple/red/cyan) left alone — they carry meaning (tool badges, status indicators)

Motion

• `html.theme-transition` class (toggled by `setTheme` in app.js) gives a smooth 180ms cross-fade on theme swap, then removes itself so individual hovers stay snappy
• `@keyframes accent-pulse` + `.cta-pulse` class — soft 2.4s glow for primary CTAs
• `[data-reveal]` opt-in scaffold for fade-up entry animations (pure CSS, no JS hooked up yet — additive follow-up)
• `prefers-reduced-motion` short-circuits all of the above

Typography

• `<link rel="stylesheet" ...family=Inter...">` in `index.html`
• Body font: `'Inter', -apple-system, ..., sans-serif` (graceful fallback if Google Fonts unreachable)
• `-webkit-font-smoothing: antialiased` for crisper rendering on Retina

CSP (`src/server.js`)

• `style-src` relaxed to include `https://fonts.googleapis.com\`
• `font-src` adds `https://fonts.gstatic.com\`
• All other directives (connect-src 'self', frame-ancestors 'none', etc.) untouched

Verified

• `node -c` clean on `src/server.js` and `src/frontend/app.js`
• `node --test test/*.test.js` → 144/0/2 (no regressions)
• Dark theme — palette, Inter, neon green confirmed via Playwright screenshot
• Light theme — cool off-white + AA-safe accent confirmed
• Monokai — preserved unchanged (`--accent-green: #a6e22e` still wins on `[data-theme="monokai"]`)
• CSP no longer blocks the font (`document.fonts.check('1em Inter')` → `true`)

Diff size

4 files, +90/-21 — mostly CSS variable values in two `:root` blocks.

What this does NOT do

• ❌ No React / Tailwind / build step — zero-deps vanilla-JS architecture preserved
• ❌ No component restructure — sidebar/cards/buttons keep their existing markup
• ❌ Monokai theme not touched
• ❌ Semantic accent colors (blue/orange/purple/red/cyan) not changed — they still differentiate tool badges and statuses