feat: replace print() calls with Python logging module

[Aditya8840]

Summary

Closes #2

• Replace all 11 print() calls across agent.py and main.py with properly-leveled logging.getLogger("droidpilot") calls (INFO, WARNING, ERROR, DEBUG)
• Add _setup_logging() helper in main.py with clean format (no timestamps for TTY, timestamps for file/verbose output)
• Add --verbose (-v) and --quiet (-q) mutually exclusive CLI flags to control output verbosity

Changes

droidpilot/main.py

• Added _setup_logging(verbose, quiet) helper configuring the droidpilot logger
• Added -v/--verbose flag (DEBUG level + timestamps) and -q/--quiet flag (WARNING level only)
• Replaced print(..., file=sys.stderr) error output with logger.error()
• Replaced print() status messages with logger.info()
• Added return type hint to main()

droidpilot/agent.py

• Added logging import and module-level logger = logging.getLogger("droidpilot")
• Replaced all print() calls with appropriate severity levels:
  • logger.info() for device info, task, step progress, and completion
  • logger.warning() for UI read failures and missing actions
  • logger.debug() for action result details

Test plan

• Run droidpilot "test" — should show INFO-level output without timestamps
• Run droidpilot -v "test" — should show DEBUG-level output with timestamps
• Run droidpilot -q "test" — should only show warnings and errors
• Run droidpilot "test" 2>debug.log — log file should contain timestamps
• Verify -v and -q are mutually exclusive (parser rejects both)

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