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/types.ts

@@ -120,6 +120,35 @@ export interface SourceResponse {
   options: Options
 }
 
+/** How a source daemon is reached. 'local' is the built-in, unremovable one. */
+export type SourceKind = 'local' | 'docker' | 'ssh'
+
+export interface Source {
+  id: string
+  name: string
+  kind: SourceKind
+  /** Daemon address for the 'docker' kind, e.g. tcp://10.0.0.5:2375. */
+  dockerHost?: string
+  /** Remote host for the 'ssh' kind; the same shape as a target connection. */
+  ssh?: Connection
+}
+
+export interface SourceStatus {
+  id: string
+  name: string
+  kind: SourceKind
+  endpoint: string
+  dockerVersion?: string
+  connected: boolean
+  error?: string
+}
+
+export interface SourcesResponse {
+  sources: Source[]
+  selected: string
+  current: SourceStatus | null
+}
+
 export type AuthMethod = 'password' | 'key' | 'agent'
 
 export interface Connection {
@@ -253,6 +282,7 @@ export interface Health {
   dockerHost: string
   dockerVersion?: string
   dockerError?: string
+  source?: SourceStatus
   packageDir: string
   dataDir: string
   knownHosts: string