Add tmux pane management for background agent sessions (#1094)

* feat(config): add TmuxConfigSchema for tmux subagent pane management

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

* feat(shared): add tmux module structure

* feat(shared/tmux): implement tmux pane utilities

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

* test(tmux-subagent): add TmuxSessionManager tests (TDD RED)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

* feat(tmux-subagent): implement TmuxSessionManager

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

* feat(integration): wire TmuxSessionManager with 500ms delay

- Task 5: Add 500ms delay in BackgroundManager after session creation
- Task 6: Wire TmuxSessionManager event handlers (session.created/deleted)
- Both changes integrate tmux pane management into plugin lifecycle

Co-authored-by: Sisyphus <ultrawork@oh-my-opencode>

---------

Co-authored-by: justsisyphus <justsisyphus@users.noreply.github.com>
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
Co-authored-by: Sisyphus <ultrawork@oh-my-opencode>

assets/oh-my-opencode.schema.json

@@ -2186,6 +2186,32 @@
           ]
         }
       }
+    },
+    "tmux": {
+      "type": "object",
+      "properties": {
+        "enabled": {
+          "default": false,
+          "type": "boolean"
+        },
+        "layout": {
+          "default": "main-vertical",
+          "type": "string",
+          "enum": [
+            "main-horizontal",
+            "main-vertical",
+            "tiled",
+            "even-horizontal",
+            "even-vertical"
+          ]
+        },
+        "main_pane_size": {
+          "default": 60,
+          "type": "number",
+          "minimum": 20,
+          "maximum": 80
+        }
+      }
     }
   }
 }