Small changes to colors and style to new UI

[javuto]

Restore the rail circuit background, enlarge the nav identity, separate data surfaces

Three visual corrections, all frontend-only. No behaviour, API or data changes.

1. Restored the circuit background on the side nav

The rail's circuit-trace texture had been reimplemented as a mask-image at opacity: 0.055, which renders as very nearly nothing. Restored the v0.5.7 block verbatim: .sidenav-circuit with the tiled inline-SVG background-image in brand teal — #2bc4be at 0.08 in dark, #0a8a85 at 0.10 in light, alphas tuned per theme so both read at similar perceived density — layered under the teal sheen gradient at the top of the rail.

SideNav.tsx references the release class name (sidenav-circuit) again; the isolation/z-index scaffolding the mask version needed is gone with it, since background-image composes directly.

2. Bigger, centered product identity in the nav

The mark and wordmark were a 24px logo beside 15px text, left-aligned. They're now stacked and centered: 44px logo over a 20px wordmark. Stacking is what allows both to grow without widening the rail. Collapsed mode centers a 28px mark with the wordmark hidden, as before.

3. Data surfaces now sit a tone above the page

Root cause: AppShell's main content area gained bg-[color:var(--bg-1)] at some point after v0.5.7, where it had been transparent over the shell's --bg-0. Every panel is also --bg-1, so panels ended up on a same-toned page with only their borders separating them — the flat look this fixes.

Rather than reverting the page background (which would undo the newer rounded-card shell treatment), the data surfaces move up a tone. Applied in two passes, in this order, so nothing collided:

1. Existing --bg-2 elements inside those files → --bg-3. These are table header rows, badges and hover states; left alone they would have disappeared into the newly---bg-2 panels around them.
2. Container panels (border + --bg-1) → --bg-2.

Scope: 33 files across src/features/** plus components/data/StatCard.tsx.

Deliberately excluded:

• Chrome and controls — DropdownMenu, Pagination, EnvSwitcher, SideNavPreview stay at --bg-1. A floating menu should read as elevated above the page, not sunk into it.
• LoginPage — the sweep initially caught it and the result was wrong. It's a standalone screen with its own cyber-grid and card-glow treatment, not a data surface on the app shell. Reverted.

Changes

• frontend/src/styles/base.css — .sidenav-circuit restored from v0.5.7
• frontend/src/components/chrome/SideNav.tsx — class name, stacked/centered identity at 44px + 20px
• 33 files across src/features/** and components/data/StatCard.tsx — panel tone shift

Testing

• Full suite green: 292 tests, tsc clean.
• StatCard.test.tsx pinned the card surface to --bg-1. The test's actual intent is "flat surface, no decorative gradient", so the no-gradient assertion is untouched and only the token moved, with a comment recording why data surfaces sit above the page.

Note for reviewers

Worth an eyeball in the browser before merging. The step is #171717 → #1b1b1b in dark and #ffffff → #fcfcfc in light — intentionally gentle, but the light-theme delta is very subtle. If it reads as no change there, the fix is nudging the light --bg-2 token a shade rather than revisiting 33 files.