feat: add path completion, LCP-based suggestions, and validator tests

- Refactored `FalyxCompleter` to support longest common prefix (LCP) completions by default.
- Added `_ensure_quote` helper to auto-quote completions containing spaces/tabs.
- Integrated `_yield_lcp_completions` for consistent completion insertion logic.
- Added `_suggest_paths()` helper to dynamically suggest filesystem paths for arguments of type `Path`.
- Integrated path completion into `suggest_next()` for both positional and flagged arguments.
- Updated `argument_examples.py` to include a `--path` argument (`Path | None`), demonstrating file path completion.
- Enabled `CompleteStyle.COLUMN` for tab-completion menu formatting in interactive sessions.
- Improved bottom bar docstring formatting with fenced code block examples.
- Added safeguard to `word_validator` to reject `"N"` since it’s reserved for `yes_no_validator`.
- Improved help panel rendering for commands (using `Padding` + `Panel`).
- Added full test coverage for:
  - `FalyxCompleter` and LCP behavior (`tests/test_completer/`)
  - All validators (`tests/test_validators/`)
- Bumped version to 0.1.80.

tests/test_completer/test_lcp_completions.py

@@ -0,0 +1,38 @@
+from types import SimpleNamespace
+
+import pytest
+from prompt_toolkit.document import Document
+
+from falyx.completer import FalyxCompleter
+
+
+@pytest.fixture
+def fake_falyx():
+    fake_arg_parser = SimpleNamespace(
+        suggest_next=lambda tokens, end: ["AETHERWARP", "AETHERZOOM"]
+    )
+    fake_command = SimpleNamespace(key="R", aliases=["RUN"], arg_parser=fake_arg_parser)
+    return SimpleNamespace(
+        exit_command=SimpleNamespace(key="X", aliases=["EXIT"]),
+        help_command=SimpleNamespace(key="H", aliases=["HELP"]),
+        history_command=SimpleNamespace(key="Y", aliases=["HISTORY"]),
+        commands={"R": fake_command},
+        _name_map={"R": fake_command, "RUN": fake_command, "X": fake_command},
+    )
+
+
+def test_lcp_completions(fake_falyx):
+    completer = FalyxCompleter(fake_falyx)
+    doc = Document("R A")
+    results = list(completer.get_completions(doc, None))
+    assert any(c.text == "AETHER" for c in results)
+    assert any(c.text == "AETHERWARP" for c in results)
+    assert any(c.text == "AETHERZOOM" for c in results)
+
+
+def test_lcp_completions_space(fake_falyx):
+    completer = FalyxCompleter(fake_falyx)
+    suggestions = ["London", "New York", "San Francisco"]
+    stub = "N"
+    completions = list(completer._yield_lcp_completions(suggestions, stub))
+    assert any(c.text == '"New York"' for c in completions)