fix(terminal): start PTY before viewport mounts without dropping output or startup replies

Terminal creation no longer waits for the Ghostty viewport to report its
size: it starts the PTY immediately with a container/font-derived
provisional size (falling back to 80x24), then resizes once the real
viewport dimensions are known, with a dedupe guard while sizing settles.

Starting the shell earlier means it can emit device/theme queries before
a browser terminal is attached to answer them, so the server now answers
primary device attribute queries itself (Fish blocks ~10s on this at
startup) and bun-pty buffers output emitted before a data subscriber
attaches. Also fixes a few WebSocket transport reconnect races surfaced
by session creation now overlapping renderer setup.

packages/web/server/lib/terminal/theme-response.test.js

@@ -44,4 +44,27 @@ describe('terminal theme responses', () => {
       '\u001b]10;rgb:1b1b/1b1b/1b1b\u001b\\',
     ]);
   });
+
+  test('answers a primary device attribute query when the fallback is enabled', () => {
+    const attached = consumeTerminalThemeQueries('', '\u001b[0c', lightAppearance);
+    const unattached = consumeTerminalThemeQueries('', '\u001b[0c', lightAppearance, {
+      respondToPrimaryDeviceAttributes: true,
+    });
+
+    expect(attached.responses).toEqual([]);
+    expect(unattached.responses).toEqual(['\u001b[?1;2c']);
+  });
+
+  test('answers a primary device attribute query split across PTY chunks', () => {
+    const first = consumeTerminalThemeQueries('', '\u001b[0', lightAppearance, {
+      respondToPrimaryDeviceAttributes: true,
+    });
+    const second = consumeTerminalThemeQueries(first.pending, 'c', {
+      ...lightAppearance,
+      modeEnabled: first.modeEnabled,
+    }, { respondToPrimaryDeviceAttributes: true });
+
+    expect(first.pending).toBe('\u001b[0');
+    expect(second.responses).toEqual(['\u001b[?1;2c']);
+  });
 });