feat: switch to uv, add check command, fix silent a11y failures

- Added pyobjc-framework-ApplicationServices to dependencies (was
  implicitly available via pyenv's system packages but missing in
  clean venvs)
- Added `cursor-flasher check` command that verifies Cursor is running
  and accessibility permissions are working
- Detector now logs a warning when a11y tree reads fail (previously
  failed silently, making permission issues invisible)
- Switched to uv for dependency management: `uv sync` + `uv run`
- Updated README with uv-based workflow and accessibility
  troubleshooting guide

Made-with: Cursor

pyproject.toml

@@ -8,6 +8,7 @@ version = "0.1.0"
 description = "Flash Cursor's window when the AI agent is waiting for input"
 requires-python = ">=3.10"
 dependencies = [
+    "pyobjc-framework-applicationservices>=12.1",
     "pyobjc-framework-Cocoa",
     "pyobjc-framework-Quartz",
     "PyYAML",
@@ -21,3 +22,6 @@ cursor-flasher = "cursor_flasher.cli:main"
 
 [tool.setuptools.packages.find]
 where = ["src"]
+
+[tool.uv]
+dev-dependencies = ["pytest", "pytest-mock"]