Add per-capsule stats detail page with live CPU/RAM charts

- New detail page at /dashboard/capsules/[id] with Stats and Files tabs
- Stats tab shows capsule info card (status, template, CPU, memory, disk,
  started, idle timeout) and two stacked Chart.js charts with live values
- Metrics API client with 10s polling and moving-average smoothing
- Capsule ID in list table is now a clickable link to the detail page
- Layout breadcrumb header (Capsules > sb-xxx) with back navigation
- Fix metrics sampler: use v.PID() directly as Firecracker PID since
  unshare -m execs (not forks) through the bash/ip-netns-exec/firecracker
  chain, so all share the same PID. Removes unused findChildPID.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/api/capsules.ts

@@ -20,6 +20,10 @@ export async function listCapsules(): Promise<ApiResult<Capsule[]>> {
 	return apiFetch('GET', '/api/v1/sandboxes');
 }
 
+export async function getCapsule(id: string): Promise<ApiResult<Capsule>> {
+	return apiFetch('GET', `/api/v1/sandboxes/${id}`);
+}
+
 export type CreateCapsuleParams = {
 	template?: string;
 	vcpus?: number;