core/config: add the [notify] section

`[notify]` decides what the CLI does when a prompt is waiting on the human:
`grace_seconds` (default 5s, roughly Claude Code's permission notice) before
anything is shown, `min_interval_seconds` between two notifications,
`channels` (`auto` = desktop then terminal), `actions` for the allow/deny/review
buttons, `include_reason` for the one-line reason, and `protocol` to pin the
terminal escape protocol.

The reason stays out by default because it names commands, argv and URLs, and a
notification outlives the prompt and may be mirrored to a lock screen. Unknown
keys degrade to the defaults, the way `[mcp]` does, and `reload()` re-reads the
section.

Desktop notifications need the optional `notify` extra (`desktop-notifier`),
which is the only new dependency and stays off the default install.

tests/test_config/test_notify_section.py

@@ -0,0 +1,81 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from plyngent.config import load
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+
+def test_notify_section_defaults(tmp_path: Path) -> None:
+    """Notifications are on by default: a five-second grace, desktop first."""
+    path = tmp_path / "c.toml"
+    _ = path.write_text("", encoding="utf-8")
+    cfg = load(path).notify_config
+    assert cfg.enabled is True
+    assert cfg.grace_seconds == 5.0
+    assert cfg.min_interval_seconds == 10.0
+    assert cfg.channels == ["auto"]
+    assert cfg.actions is True
+    assert cfg.include_reason is False
+    assert cfg.protocol == ""
+
+
+def test_notify_section_parse(tmp_path: Path) -> None:
+    path = tmp_path / "c.toml"
+    _ = path.write_text(
+        """
+[notify]
+enabled = false
+grace_seconds = 2.5
+min_interval_seconds = 30.0
+channels = ["terminal"]
+actions = false
+include_reason = true
+protocol = "osc9"
+""",
+        encoding="utf-8",
+    )
+    cfg = load(path).notify_config
+    assert cfg.enabled is False
+    assert cfg.grace_seconds == 2.5
+    assert cfg.min_interval_seconds == 30.0
+    assert cfg.channels == ["terminal"]
+    assert cfg.actions is False
+    assert cfg.include_reason is True
+    assert cfg.protocol == "osc9"
+
+
+def test_notify_section_typo_falls_back(tmp_path: Path) -> None:
+    """An unknown key or a bad type degrades to the defaults, like ``[mcp]``."""
+    path = tmp_path / "c.toml"
+    _ = path.write_text(
+        """
+[notify]
+grace = 1.0
+""",
+        encoding="utf-8",
+    )
+    assert load(path).notify_config.grace_seconds == 5.0
+
+    path2 = tmp_path / "d.toml"
+    _ = path2.write_text(
+        """
+[notify]
+enabled = "yes"
+""",
+        encoding="utf-8",
+    )
+    assert load(path2).notify_config.enabled is True
+
+
+def test_notify_section_survives_reload(tmp_path: Path) -> None:
+    path = tmp_path / "c.toml"
+    _ = path.write_text("[notify]\nenabled = false\n", encoding="utf-8")
+    store = load(path)
+    assert store.notify_config.enabled is False
+    _ = path.write_text("[notify]\nenabled = true\ngrace_seconds = 1.0\n", encoding="utf-8")
+    store.reload()
+    assert store.notify_config.enabled is True
+    assert store.notify_config.grace_seconds == 1.0