GRM-13: feat: replace print() with stdlib logging module

- Create logging_config.py with get_logger() providing dual handlers:
  - Console handler (stderr) controlled by GRM_LOG_LEVEL env var (default INFO)
  - File handler (~/.local/state/grm/logs/grm.log) capturing everything at DEBUG
- Replace all print() calls in executor.py and report.py with logger.info()/error()
- Add error logging before raising AnsibleError in executor.run()
- Add GRM_LOG_LEVEL to README configuration table and logging documentation
- Update all unit tests to mock logger instead of using capsys
- 114 tests, 100% coverage, pyright clean, ruff clean

src/gitea_runner_manager/executor.py

@@ -10,6 +10,7 @@ from pathlib import Path
 
 from .exceptions import AnsibleError
 from .i18n import _
+from .logging_config import get_logger
 
 
 class AnsibleExecutor:
@@ -17,31 +18,32 @@ class AnsibleExecutor:
 
     def __init__(self, log_dir: Path | None = None) -> None:
         self._log_dir = log_dir or Path.home() / ".local" / "state" / "grm" / "logs"
+        self._logger = get_logger()
 
     def run(self, cmd: list[str], description: str = "") -> None:
         """Run an Ansible command, redirecting output to a log file."""
         log_file = self._prepare_log(cmd)
         desc = description or _("Running Ansible playbook")
 
-        print(f"[GRM] {desc}")
-        print(f"[GRM] {_('Full log: {log_file}', log_file=log_file)}")
+        self._logger.info(desc)
+        self._logger.info(_("Full log: {log_file}", log_file=log_file))
 
         returncode = self._stream(cmd, log_file)
 
         if returncode != 0:
-            raise AnsibleError(
-                _(
-                    "Ansible failed with exit code {code}. See full log: {log_file}",
-                    code=returncode,
-                    log_file=log_file,
-                )
+            msg = _(
+                "Ansible failed with exit code {code}. See full log: {log_file}",
+                code=returncode,
+                log_file=log_file,
             )
+            self._logger.error(msg)
+            raise AnsibleError(msg)
 
         status = self._extract_status(log_file)
         if status:
-            print(f"[GRM] {status}")
+            self._logger.info(status)
 
-        print(f"[GRM] {_('Done. See full log: {log_file}', log_file=log_file)}")
+        self._logger.info(_("Done. See full log: {log_file}", log_file=log_file))
 
     def _prepare_log(self, cmd: list[str]) -> Path:
         """Create a log file with header."""