feat(electrobun): wire PTY daemon into terminal tabs via Electrobun RPC

- Bun process connects to agor-ptyd via PtyClient (5 retries, exponential backoff)
- RPC bridge: 5 request handlers (create/write/resize/unsubscribe/close)
- Daemon output forwarded to WebView as pty.output messages (base64 passthrough)
- Terminal.svelte: real PTY sessions via RPC instead of echo mode
- Shared RPC schema at src/shared/pty-rpc-schema.ts
- Fixed pty-client.ts protocol: base64 string for data (was number array)
- TerminalTabs passes sessionId to Terminal component

ui-electrobun/src/shared/pty-rpc-schema.ts

@@ -0,0 +1,62 @@
+/**
+ * Shared RPC schema for PTY bridge between Bun process and WebView.
+ *
+ * Bun holds the Unix socket connection to agor-ptyd; the WebView calls
+ * into Bun via requests, and Bun pushes output/close events via messages.
+ */
+
+// ── Requests (WebView → Bun, expects a response) ─────────────────────────────
+
+export type PtyRPCRequests = {
+  /** Create a PTY session and subscribe to its output. */
+  "pty.create": {
+    params: {
+      sessionId: string;
+      cols: number;
+      rows: number;
+      /** Working directory for the shell process. */
+      cwd?: string;
+    };
+    response: { ok: boolean; error?: string };
+  };
+  /** Write raw input bytes (base64-encoded) to a PTY session. */
+  "pty.write": {
+    params: {
+      sessionId: string;
+      /** UTF-8 text typed by the user (xterm onData delivers this). */
+      data: string;
+    };
+    response: { ok: boolean };
+  };
+  /** Notify the daemon that the terminal dimensions changed. */
+  "pty.resize": {
+    params: { sessionId: string; cols: number; rows: number };
+    response: { ok: boolean };
+  };
+  /** Unsubscribe from a session's output (session stays alive). */
+  "pty.unsubscribe": {
+    params: { sessionId: string };
+    response: { ok: boolean };
+  };
+  /** Kill a PTY session. */
+  "pty.close": {
+    params: { sessionId: string };
+    response: { ok: boolean };
+  };
+};
+
+// ── Messages (Bun → WebView, fire-and-forget) ────────────────────────────────
+
+export type PtyRPCMessages = {
+  /** PTY output chunk. data is base64-encoded raw bytes from the daemon. */
+  "pty.output": { sessionId: string; data: string };
+  /** PTY session exited. */
+  "pty.closed": { sessionId: string; exitCode: number | null };
+};
+
+// ── Combined schema ───────────────────────────────────────────────────────────
+
+export type PtyRPCSchema = {
+  requests: PtyRPCRequests;
+  messages: PtyRPCMessages;
+};