feat: redesign help command, improve completer UX, and document Falyx CLI

- Renamed CLI subcommand from `list` to `help` for clarity and discoverability.
- Added `--key` and `--tldr` support to the `help` command for detailed and example-based output.
- Introduced `FalyxMode.HELP` to clearly delineate help-related behavior.
- Enhanced `_render_help()` to support:
  - Tag filtering (`--tag`)
  - Per-command help (`--key`)
  - TLDR example rendering (`--tldr`)
- Updated built-in Help command to:
  - Use `FalyxMode.HELP` internally
  - Provide fallback messages for missing help or TLDR data
  - Remove `LIST` alias (replaced by `help`)
- Documented `FalyxCompleter`:
  - Improved docstrings for public methods and completions
  - Updated internal documentation to reflect all supported completion cases
- Updated `CommandArgumentParser.render_tldr()` with fallback message for missing TLDR entries.
- Updated all parser docstrings and variable names to reference `help` (not `list`) as the proper CLI entrypoint.
- Added test coverage:
  - `tests/test_falyx/test_help.py` for CLI `help` command with `tag`, `key`, `tldr`, and fallback scenarios
  - `tests/test_falyx/test_run.py` for basic CLI parser integration
- Bumped version to 0.1.81

tests/test_falyx/test_run.py

@@ -0,0 +1,19 @@
+import sys
+
+import pytest
+
+from falyx import Falyx
+from falyx.parser import get_arg_parsers
+
+
+@pytest.mark.asyncio
+async def test_run_basic(capsys):
+    sys.argv = ["falyx", "run", "-h"]
+    falyx_parsers = get_arg_parsers()
+    assert falyx_parsers is not None, "Falyx parsers should be initialized"
+    flx = Falyx()
+    with pytest.raises(SystemExit):
+        await flx.run(falyx_parsers)
+
+    captured = capsys.readouterr()
+    assert "Run a command by its key or alias." in captured.out