Normalize iTerm2 session ID alias handling

[mkusaka]

Summary

Normalize iTerm2 session ID aliases before session lookup so CLI commands accept both shell-facing IDs and canonical API IDs.

Changes

• Add normalize_session_id in src/it2/core/session_handler.py to convert w<window>t<tab>p<pane>:<GUID> and w<window>t<tab>p<pane>.<GUID> into canonical GUIDs.
• Add get_session_by_id helper in src/it2/core/session_handler.py and route session resolution through this helper.
• Update session focus in src/it2/commands/session.py to use normalized lookup.
• Update profile apply in src/it2/commands/profile.py to use normalized lookup.
• Update app broadcast add in src/it2/commands/app.py to use normalized lookup.
• Add/extend tests in tests/test_session_handler.py, tests/test_session_commands.py, tests/test_profile_commands.py, and tests/test_app_commands.py to cover alias formats.
• Add detailed helper comments/docstrings with iTerm2 implementation context (shell/env alias format vs API exact-match behavior).

Why

iTerm2 often exposes session IDs via shell integration values (e.g. ITERM_SESSION_ID and session.termid) that include window/tab/pane prefixes. The Python API lookup uses exact Session.session_id GUID matching, so alias IDs can fail even when the session exists.

Notes

• Special selectors active and all remain unchanged.
• A fallback lookup with the original input is kept to reduce risk if iTerm2 introduces additional ID shapes.
• CI formatting failure was addressed by applying black formatting to tests/test_session_commands.py.

Testing

• uv run --with ruff ruff check src tests
• uv run --with mypy --with types-PyYAML mypy src
• uv run --with black black --check .
• uv run --with pytest-asyncio pytest -q tests/test_session_handler.py tests/test_session_commands.py tests/test_profile_commands.py tests/test_app_commands.py
• GitHub Actions run passed: https://github.com/mkusaka/it2/actions/runs/21803781233