feat: structured DEBUG/INFO logging via loguru

- common/logging.py: improve format to timestamp|LEVEL|module:func:line - message
- core/ layer: DEBUG log every subprocess invocation (cmd, rc, byte counts),
  JSON load/dump events, parsed application_id. ERROR log on failures.
- tools/ layer: DEBUG log every public tool entry with key parameters,
  INFO log on business outcomes (saved/submitted/killed/...).
- New tests/unit/test_logging.py: capture loguru output via in-memory sink
  and assert DEBUG + INFO messages are emitted for representative flows.

common/logging.py

@@ -1,10 +1,29 @@
 # coding=utf-8
 """
 @Time   :2026/6/24
-@Author :tao.chen 
+@Author :tao.chen
+
+Process-wide loguru configuration. Import `logger` from here in every
+module instead of instantiating new loggers.
+
+Levels used in this project:
+  DEBUG  - entry/exit of public tools, subprocess commands, file I/O paths
+  INFO   - business events (job submitted, status changed, connection saved)
+  WARNING - recoverable problems (transient YARN issues, retry-able)
+  ERROR  - raised exceptions (caller will see the traceback)
 """
 import sys
+
 from loguru import logger
 
 logger.remove()
-logger.add(sys.stderr, level="DEBUG")
+logger.add(
+    sys.stderr,
+    level="DEBUG",
+    format=(
+        "<green>{time:HH:mm:ss.SSS}</green> | "
+        "<level>{level: <7}</level> | "
+        "<cyan>{name}</cyan>:<cyan>{function}</cyan>:<cyan>{line}</cyan> - "
+        "<level>{message}</level>"
+    ),
+)