sidecar self-registration: sidecars connect to API server instead of vice versa

Flips the connection model so sidecars register themselves with the API
server via WebSocket at /api/sidecar/register, enabling dynamic discovery,
location independence, and automatic reconnection from either side.

- Add registration protocol types and PTY command/event types
- Create sidecar-registry.ts (replaces sidecar-client.ts) as passive registry
- Create sidecar connector (connect.ts) with exponential backoff reconnect
- Convert process sidecar from WS server to WS client
- Convert PTY sidecar from WS server to multiplexed WS client
- Simplify terminal bridge to thin adapter using registry
- Add PTY sidecar as PM2-managed process
- Update all consumer imports

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ecosystem.config.cjs

@@ -1,5 +1,11 @@
 module.exports = {
   apps: [
+    {
+      name: 'officer',
+      script: 'bun',
+      args: 'start',
+      watch: false,
+    },
     {
       name: 'officer-sidecar',
       script: 'bun',
@@ -7,9 +13,9 @@ module.exports = {
       watch: false,
     },
     {
-      name: 'officer',
-      script: 'bun',
-      args: 'start',
+      name: 'officer-pty',
+      script: 'node',
+      args: 'src/servers/api/terminal/pty-sidecar.mjs',
       watch: false,
     },
   ],