dashboard: slug to page footer, not chrome (#389 follow-up)

PR #392 moved the slug below the tab strip but kept it INSIDE the
sticky chrome — Mara's report ("still at old position everywhere
except flow tab") makes the original intent clearer: the slug
should be at the page BOTTOM, with the chrome reduced to pure
navigation.

## index.html
- Remove the banner-thin from `.dashboard-chrome` entirely.
- Move it into the existing `<footer>` element (above the divider
  + project-link line). Sits at the bottom of every tab pane after
  the main content scrolls past.

## flow.html
- Remove the banner-thin from the chrome. The flow page is a
  full-viewport terminal with `body { overflow: hidden }` and
  no normal-flow footer position — the slug simply doesn't appear
  here. The frosted chrome is purely the tab strip now.

## dashboard.css
- `--flow-header-h: 4.7em → 3.6em` — chrome is shorter without
  the banner; terminal padding-top + tail-pill offset + inbox-pill
  top all derive from this variable, so they follow automatically.
- `footer .banner-thin { margin-bottom: 0.8em }` so the slug
  doesn't crash into the divider + link line below it.

No JS changes. Build clean.

frontend/packages/dashboard/src/dashboard.css

@@ -1211,6 +1211,12 @@ footer {
   font-size: 0.9em;
 }
 footer a { color: var(--purple); }
+/* Slug banner now lives at the page footer (#389 follow-up) — give
+   it a slim top margin so it doesn't crash into the prior content,
+   and bottom margin separating from the divider/link line. */
+footer .banner-thin {
+  margin-bottom: 0.8em;
+}
 
 /* ─── side panel ─────────────────────────────────────────────────
    Long content (file previews, diffs, journald, applied config)
@@ -1348,12 +1354,13 @@ footer a { color: var(--purple); }
    ergonomics without stealing terminal real estate. */
 
 :root {
-  /* Approximate height of the flow chrome (banner-thin + tabbar +
-     dashboard-chrome padding). Bumped slightly above the natural
-     content height so the terminal padding-top clears the bottom
-     border. Tweaked once after #383 took over the chrome from the
-     simpler title bar. */
-  --flow-header-h: 4.7em;
+  /* Approximate height of the flow chrome (tabbar + dashboard-chrome
+     padding). The banner-thin slug used to live in the chrome and
+     padded this up to 4.7em; with the slug moved out (#389 follow-up:
+     slug lives at the page footer on /, simply omitted on /flow.html
+     since there's no normal-flow footer position in the full-viewport
+     terminal), the chrome is just tabs now and shrinks accordingly. */
+  --flow-header-h: 3.6em;
   --flow-composer-h: 3.6em;
   --flow-frost-bg: rgba(30, 30, 46, 0.74);
   --flow-frost-blur: blur(12px) saturate(140%);