feat(help): enhance CLI help rendering with Panels and TLDR validation

- Updated `Command.help_signature` to return a `(Panel, description)` tuple,
  enabling richer Rich-based help output with formatted panels.
- Integrated `program` context into commands to display accurate CLI invocation
  (`falyx run …`) depending on mode (RUN, PREVIEW, RUN_ALL).
- Refactored `_show_help` to print `Panel`-styled usage and descriptions instead
  of table rows.
- Added `program` and `options_manager` propagation to built-in commands
  (Exit, History, Help) for consistent CLI display.
- Improved `CommandArgumentParser.add_tldr_examples()` with stricter validation
  (`all()` instead of `any()`), and added new TLDR tests for coverage.
- Simplified parser epilog text to `Tip: Use 'falyx run ?' to show available commands.`
- Added tests for required `Argument` fields and TLDR examples.
- Bumped version to 0.1.73.

tests/test_parsers/test_argument.py

@@ -88,3 +88,11 @@ def test_argument_equality():
     assert arg != "not an argument"
     assert arg is not None
     assert arg != object()
+
+
+def test_argument_required():
+    arg = Argument("--foo", dest="foo", required=True)
+    assert arg.required is True
+
+    arg2 = Argument("--bar", dest="bar", required=False)
+    assert arg2.required is False