feat: add SSH integration wrapper for shell integration

- Implements opt-in SSH wrapper following sudo pattern
- Supports term_only, basic, and full integration levels
- Fixes xterm-ghostty TERM compatibility on remote systems
- Propagates shell integration environment variables
- Allows for automatic installation of terminfo if desired
- Addresses GitHub discussions #5892 and #4156

src/termio/shell_integration.zig

@@ -45,6 +45,7 @@ pub fn setup(
     env: *EnvMap,
     force_shell: ?Shell,
     features: config.ShellIntegrationFeatures,
+    ssh_integration: config.SSHIntegration,
 ) !?ShellIntegration {
     const exe = if (force_shell) |shell| switch (shell) {
         .bash => "bash",
@@ -70,8 +71,9 @@ pub fn setup(
         exe,
     );
 
-    // Setup our feature env vars
+    // Setup our feature env vars and SSH integration
     try setupFeatures(env, features);
+    try setupSSHIntegration(env, ssh_integration);
 
     return result;
 }
@@ -159,6 +161,7 @@ test "force shell" {
             &env,
             shell,
             .{},
+            .off,
         );
         try testing.expectEqual(shell, result.?.shell);
     }
@@ -224,6 +227,15 @@ test "setup features" {
     }
 }
 
+pub fn setupSSHIntegration(
+    env: *EnvMap,
+    ssh_integration: config.SSHIntegration,
+) !void {
+    if (ssh_integration != .off) {
+        try env.put("GHOSTTY_SSH_INTEGRATION", @tagName(ssh_integration));
+    }
+}
+
 /// Setup the bash automatic shell integration. This works by
 /// starting bash in POSIX mode and using the ENV environment
 /// variable to load our bash integration script. This prevents