refactor: move preset command handlers to presets/_commands.py (PR-6/8)

Cut the preset_app / preset_catalog_app Typer groups and all 12 command
handlers out of __init__.py into presets/_commands.py, exposing register(app)
— mirrors the integration co-location from PR-5. __init__.py now registers
via _register_preset_cmds(app), dropping ~620 lines (3282 -> 2663).

Handlers lazy-import root helpers (_require_specify_project, get_speckit_version,
_locate_bundled_preset, _display_project_path) via 'from .. import' so test
monkeypatching of specify_cli.<helper> keeps working. _locate_bundled_preset
kept as an explicit re-export in __init__.py for that resolution path.

CLI surface and public imports unchanged. Full suite: 3162 passed, 40 skipped.

Author: darion-yaphet