swarm-ui: page shell + layout primitives

Structural foundation split out of hyperhive#3118 per mara's steer:
structure first so the real overview page (hive roster) and later
routes (swarm-wide agent roster) land as content changes rather than
each reinventing chrome + nav + a table/panel/chip shape.

- <Shell>: header bar (branding) + nav row, wraps every route. Route
  list lives in Shell itself (one small SPA, one place to know its
  own nav).
- ui/Panel, ui/StatusChip, ui/Table: the three primitives the
  overview page's actual scope (hive roster: name/domain/status,
  linking out to each hive's own dashboard) calls for, nothing
  speculative beyond that.

Preact-native styling (plain CSS files imported via swarm-ui.css, no
shadow DOM — this package renders into light DOM) — not
@hive/shared's chrome.css, which is the old MPA dashboard's visual
language. Same base16/Catppuccin color tokens via theme.css/colors.css
so it still reads as hyperhive.

npm run build (whole frontend workspace) + npm run typecheck both
clean. Verified with a real headless-chromium screenshot against the
built dist, not just source-reading.

Fixes hyperhive#3211

frontend/packages/swarm-ui/src/swarm-ui.css

@@ -1,12 +1,5 @@
 @import "@hive/shared/base.css";
-
-/* Bootstrap placeholder only — real layout comes with the first
-   route that actually needs one. */
-.swarm-ui-empty {
-  max-width: 40em;
-  margin: 4em auto;
-  padding: 0 1em;
-}
-.swarm-ui-empty h1 {
-  color: var(--purple);
-}
+@import "./shell/Shell.css";
+@import "./ui/Panel.css";
+@import "./ui/StatusChip.css";
+@import "./ui/Table.css";