fix: Add uv tool bin to PATH after installation

On fresh machines, after 'uv tool install amplifier' succeeds, the
amplifier binary may not be in the current shell's PATH. This caused
the confusing output:
  '✓ Amplifier CLI installed'
  'Failed to install Amplifier CLI'

The fix ensures ~/.local/bin (uv's default tool location) is added
to the current process's PATH before checking if amplifier exists.

🤖 Generated with [Amplifier](https://github.com/microsoft/amplifier)

Co-Authored-By: Amplifier <[email protected]>

Author: rysweet

src/amplihack/launcher/amplifier.py

@@ -10,8 +10,42 @@
 from pathlib import Path
 
 
+def get_uv_tool_bin_dir() -> Path | None:
+    """Get the uv tool bin directory."""
+    # Try common locations
+    candidates = [
+        Path.home() / ".local" / "bin",  # Linux/macOS default
+        Path.home() / ".cargo" / "bin",  # Alternative location
+    ]
+    
+    # Also check UV_TOOL_BIN_DIR environment variable
+    if env_dir := os.environ.get("UV_TOOL_BIN_DIR"):
+        candidates.insert(0, Path(env_dir))
+    
+    for candidate in candidates:
+        if candidate.exists() and (candidate / "amplifier").exists():
+            return candidate
+    
+    # Return first candidate even if amplifier not there yet (for post-install)
+    for candidate in candidates:
+        if candidate.exists():
+            return candidate
+    
+    return None
+
+
+def ensure_uv_bin_in_path() -> None:
+    """Ensure uv tool bin directory is in PATH for current process."""
+    bin_dir = get_uv_tool_bin_dir()
+    if bin_dir and str(bin_dir) not in os.environ.get("PATH", ""):
+        os.environ["PATH"] = f"{bin_dir}:{os.environ.get('PATH', '')}"
+
+
 def check_amplifier() -> bool:
     """Check if Amplifier CLI is installed."""
+    # Ensure uv bin dir is in PATH
+    ensure_uv_bin_in_path()
+    
     try:
         result = subprocess.run(
             ["amplifier", "--version"], capture_output=True, timeout=5, check=False