swarm-ui: colocate component CSS as JS-side-effect imports

Per mara's review question on PR#3219 ('shouldnt the jsx files import
their css?'): each component now does its own import ('./Shell.css',
'./Panel.css', ...) instead of swarm-ui.css centrally @import-ing
every component's stylesheet. esbuild folds every .css reachable from
main.tsx's import graph into one main.css companion output next to
main.js — no separate build step, this is bundle:true's existing
behavior, just not exercised until now.

swarm-ui.css keeps only the shared base reset (@hive/shared/base.css)
since that isn't any one component's concern. Added src/css.d.ts
(ambient '*.css' module) since tsc otherwise rejects a side-effect
import of a non-JS/TS specifier.

Side benefit: a component nothing imports (yet) no longer ships its
CSS either — StatusChip/Table aren't referenced from App.tsx today,
and main.css correctly only carries Shell.css + Panel.css. The old
central-import approach shipped all four unconditionally.

npm run build + typecheck clean. Re-screenshotted the real dist —
pixel-identical to before this change.

frontend/packages/swarm-ui/src/ui/panel/Panel.tsx

@@ -3,6 +3,7 @@
 // card-with-actions/footer/whatever kit — those get added the first
 // time a real page actually needs one, not speculatively ahead of it.
 import type { ComponentChildren } from 'preact';
+import './Panel.css';
 
 export function Panel({ title, children }: { title?: string; children: ComponentChildren }) {
   return (

frontend/packages/swarm-ui/src/ui/status-chip/StatusChip.tsx

@@ -4,6 +4,8 @@
 // single static "configured" tone and grows real online/stale/offline
 // states once a status rollup lands server-side — same component,
 // richer data later, no rebuild.
+import './StatusChip.css';
+
 export type ChipTone = 'neutral' | 'positive' | 'warning' | 'negative';
 
 export function StatusChip({ tone = 'neutral', label }: { tone?: ChipTone; label: string }) {

frontend/packages/swarm-ui/src/ui/table/Table.tsx

@@ -4,6 +4,7 @@
 // any particular row shape, so it stays reusable for the swarm-wide
 // agent roster later without a rewrite.
 import type { ComponentChildren } from 'preact';
+import './Table.css';
 
 export interface TableColumn<T> {
   key: string;