feat(ui): warm light theme and pre-mixed status fills

- Light mode moves to Claude's ivory/terracotta family: page #e8e5da, cards
  #f5f3ec (a notch below Claude's ivory, no pure-white step), warm
  borders and card shadow; dark mode is untouched.
- The surface ramp rises in lightness with its index in BOTH themes, so a
  card sits brighter than the page and every hover lifts instead of dims.
- Light --accent #a34a28 (the brand #cc785c is 3.1:1 on ivory); --fg-muted
  held at >=4.5:1; new --syn-* syntax tokens, dark keeps its pastels.
- Status/accent fills (bg-*/N, border-*/N) compile to color-mix against
  --tint-base instead of rgb(/a), so a chip is one colour on every surface.
- Hardcoded dark-only hovers (hover:text-white, hover:bg-white/5) replaced
  by tokens in DateTimePicker and SessionDrillIn.

ARCHITECTURE.md

@@ -470,6 +470,7 @@ graph TD
 ### Splash & loading UX
 
 - **`SplashScreen.tsx`** — rendered by `App.tsx` as a fixed full-screen overlay alongside the router. Shows once per browser session (`sessionStorage` gate, read synchronously so a repeat mount never flashes). Time-aware greeting + localized tagline/subtexts (`splash` i18n namespace, en/zh/vi/ko) + an animated node-graph brand mark on a dark backdrop (radial glow, drifting constellation, grain). The backdrop is **opaque from the first paint** (no entrance fade on the root) so the app rendered behind it never flashes through; only the inner content cascades in. Holds ~2.5 s, then fades out and unmounts; click-to-skip; honors `prefers-reduced-motion`. CSS-only keyframes, no added dependencies.
+- **Colour tokens (`client/src/index.css`, `tailwind.config.js`)** — one CSS-variable set per theme, consumed as `bg-surface-N` / `text-fg-*` / `border-border*` / `text-status-*` / `text-syntax-*`. The surface ramp encodes ELEVATION and rises in lightness with its index in BOTH themes: light mode's page is `surface-0` `#e8e5da` and a `.card` is the brighter `surface-3` `#f5f3ec` (Claude's warm ivory family rather than Radix slate — a cool near-white page reads as glare at any lightness, while dark mode stays slate + blue), so hovers lift instead of dimming. (Light mode previously used Radix slate in its native direction — index up meant darker — which put a near-white page under grey, recessed-looking cards: the "glaring and muddy at once" report.) Light `--accent` is `#a34a28` — Claude's terracotta two steps down, since the brand `#cc785c` is 3.1:1 on ivory — not dark's `#0090ff`, which is 3.3:1 on white and fails AA; `--fg-muted` is held at ≥4.5:1 because it carries timestamps and counts; `--shadow-card`, not the deliberately quiet `--border`, carries "raised" in light mode. Syntax colouring is tokenised too (`--syn-*`), dark keeping its 300-level pastels and light taking the same hues four steps darker. A hardcoded near-black panel, a `hover:text-white`, or `filter: invert(1)` on a form glyph is by definition a light-mode bug — token it, or scope it under `.dark`. Status and accent **fills** are pre-mixed rather than translucent: `tint()` in `tailwind.config.js` compiles `bg-status-success/10` and `border-status-danger/40` to `color-mix(…, rgb(var(--tint-base)))`, because an alpha tint composites with what is behind it and made one chip render as five different colours over the five surface steps. It is deliberately scoped to `backgroundColor`/`borderColor` — `text-*/NN` and `ring-*/NN` must stay translucent, and a translucent `surface` is what every scrim is made of.
 - **`Tooltip.tsx` (`GlobalTooltip`)** — mounted once by `App.tsx` beside the router. Every control in the app keeps writing the native `title="…"`; this listener upgrades it in place — on a 350 ms hover rest or immediately on keyboard focus it parks the attribute in `data-tip`, renders an anchored bubble (portal, arrow, flip above/below, viewport clamp, theme tokens so light mode is legible), and restores the attribute when it closes on pointer-out / pointer-down / scroll / resize / `Escape`. No wrapper at the call site, nothing to remember for the next `title=`, and the native tooltip plus the control's accessible name survive with JS off. `data-tip-off` opts an element out; `Tip.tsx` (cursor-following, for expanding a truncated number mid-sentence) draws the same `TOOLTIP_SURFACE`.
 - **Loading skeletons** — the shared `Skeleton` primitive (`components/Skeleton.tsx`) uses Tailwind `animate-pulse`. `Analytics.tsx` now renders a pulsing `AnalyticsChartsSkeleton` for the whole chart region while `data` is null (previously it fell back to empty/zero charts).
 - **`Workflows.tsx` `Section`** — the right-aligned section subtitle is clamped to a single line (`truncate` + `max-w` + hover `title`) so a long translation never wraps and unbalances the header; the full text stays in the section's `i` popover.