fix(ibus): raise exception on setup failure to enable fallback (#240)

* fix(ibus): raise exception on setup failure to enable fallback

- Add IBusSetupError exception class for detailed error context
- Modify _setup_engine() to raise exception instead of silent return
- Ensures text_injector.py fallback mechanism works when IBus fails
- Add unit tests for IBusSetupError and setup failure scenarios

Fixes silent IBus text injection failures on Wayland/Fedora reported in #34

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

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

* test(text-injector): add tests for IBus setup failure fallback

- Test that TextInjector falls back to xdotool when IBus fails
- Test fallback on both X11 and Wayland environments
- Test that text injection still works after IBus failure

Related to #34

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

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

---------

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

src/vocalinux/text_injection/__init__.py

@@ -4,6 +4,7 @@ Text injection module for Vocalinux
 
 from . import text_injector  # noqa: F401
 from .ibus_engine import (  # noqa: F401
+    IBusSetupError,
     IBusTextInjector,
     install_ibus_component,
     is_engine_active,

src/vocalinux/text_injection/ibus_engine.py

@@ -27,6 +27,19 @@ from typing import Optional
 
 logger = logging.getLogger(__name__)
 
+
+class IBusSetupError(RuntimeError):
+    """
+    Exception raised when IBus engine setup fails.
+
+    This exception is raised when the IBus text injector cannot be properly
+    initialized, allowing the caller to fall back to alternative text
+    injection methods.
+    """
+
+    pass
+
+
 # Check if IBus is available
 try:
     import gi
@@ -576,13 +589,14 @@ class IBusTextInjector:
 
         # Check again after installation
         if not is_engine_registered():
-            logger.error("Failed to register IBus engine")
-            return
+            raise IBusSetupError(
+                "Failed to register IBus engine. "
+                "Try running 'ibus list-engine' to verify installation."
+            )
 
         # Start the engine process (Vocalinux starts it, not IBus)
         if not start_engine_process():
-            logger.error("Failed to start IBus engine process")
-            return
+            raise IBusSetupError("Failed to start IBus engine process. Check logs for details.")
 
         # Save current engine and switch to Vocalinux
         if not is_engine_active():
@@ -594,7 +608,10 @@ class IBusTextInjector:
             if switch_engine(ENGINE_NAME):
                 logger.info("Vocalinux IBus engine activated")
             else:
-                logger.error("Failed to activate Vocalinux IBus engine")
+                raise IBusSetupError(
+                    "Failed to activate Vocalinux IBus engine. "
+                    "Try manually: ibus engine vocalinux"
+                )
 
     def stop(self) -> None:
         """