refactor: harden daemon architecture and improve standards compliance

[JacksonFergusonDev]

Summary

This PR transitions git-pulsar from a prototype script to a robust system service. It standardizes file locations, type-checks configuration, and implements atomic file operations to prevent data corruption during power loss or concurrent access.

Key Changes

1. 📂 XDG Base Directory Compliance

• Moved runtime state and logs out of ~ and into ~/.local/state/git-pulsar/ (or $XDG_STATE_HOME).
• Files affected: src/constants.py, src/service.py.

2. 🛡️ Typed Configuration

• Replaced the raw dictionary CONFIG with dataclasses (CoreConfig, LimitsConfig, etc.).
• Eliminates KeyError risks at runtime and provides structural validation on load.
• Files affected: src/daemon.py.

3. 📜 Standard Logging Implementation

• Removed: Custom manual log() function and file rotation logic.
• Added: Python's standard logging module with:
  • RotatingFileHandler for atomic log rotation.
  • Split-stream logging: stdout for interactive mode, stderr for systemd/launchd capture.
• Files affected: src/daemon.py.

4. ⚛️ Atomic Registry Operations

• Implemented an atomic "write-tmp-and-swap" pattern for prune_registry.
• Ensures the registry file is never left in a truncated or zero-byte state if the daemon crashes mid-write.
• Files affected: src/daemon.py.

5. 🧪 Test Suite Updates

• Updated test_daemon.py to mock the new CONFIG object, isolating tests from the host machine's configuration.
• Fixed a regression in test_properties.py related to newline handling in registry files.

Verification

• Unit Tests: All tests passed (uv run pytest).
• Property Tests: Hypothesis regression fixed.
• Type Check: Config dataclasses validate correctly.