Add SSH source support with dialstdio and UI components

- Implement SSH dial via stdio for remote connections
- Add sources API and storage layer for managing connection sources
- Add SourcePanel and SshFields web components for SSH configuration
- Update app structure to support source-based connections
- Update handlers and server for new sources endpoint

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

web/src/api.ts

@@ -1,6 +1,6 @@
 import type {
   Connection, Health, HostKeyInfo, JobSnapshot, PackageInfo, Plan,
-  Preflight, PreviewResponse, SourceResponse, TargetInventory,
+  Preflight, PreviewResponse, Source, SourceResponse, SourcesResponse, SourceStatus, TargetInventory,
 } from './types'
 
 // The token, when the server requires one, arrives as a query parameter the
@@ -65,6 +65,14 @@ export const api = {
   source: () => request<SourceResponse>('/api/source'),
   volumeSizes: () => request<{ volumes: Record<string, number> }>('/api/source/sizes'),
 
+  sources: () => request<SourcesResponse>('/api/sources'),
+  saveSource: (s: Partial<Source>) => post<Source>('/api/sources', s),
+  deleteSource: (id: string) => request<void>(`/api/sources/${id}`, { method: 'DELETE' }),
+  selectSource: (id: string) => post<SourceStatus>(`/api/sources/${id}/select`),
+  probeSource: (id: string) => post<HostKeyInfo>(`/api/sources/${id}/probe`),
+  trustSource: (id: string, fingerprint: string) =>
+    post<{ trusted: boolean }>(`/api/sources/${id}/trust`, { fingerprint }),
+
   connections: () => request<Connection[]>('/api/connections'),
   saveConnection: (c: Partial<Connection>) => post<Connection>('/api/connections', c),
   deleteConnection: (id: string) => request<void>(`/api/connections/${id}`, { method: 'DELETE' }),