fix: handle missing config file gracefully (no more crash on first run)

[DrGalio]

Summary

Fixes the FileNotFoundError crash when ~/.config/task-cli/config.yaml is missing. The CLI now creates a sensible default config on first run.

Changes

• task.py: load_config() now:
  • Creates ~/.config/task-cli/ directory if missing
  • Writes a default config.yaml if the file doesn't exist
  • Returns the default config content instead of crashing
• test_task.py: Added 3 new tests:
  • test_load_config_creates_default_when_missing — verifies default config is created when file is absent
  • test_load_config_reads_existing_file — verifies existing files are read correctly
  • test_load_config_handles_missing_entire_config_dir — verifies full missing-directory scenario
• .gitignore: Added Python cache exclusions

Acceptance Criteria

• No crash when config file is missing
• Creates sensible default config (matching config.yaml.example structure)
• Tests added for missing config scenario
• All 5 tests pass

Verification

# Tests pass
$ python3 -m pytest test_task.py -v
5 passed in 0.03s

# CLI works without config
$ HOME=/tmp/fake_home python3 task.py list
No tasks yet!  # ✓ No crash