Bring the docs up to the 17 Oct afternoon fixes

[saworbit]

Docs for what landed this afternoon (#1268 to #1291). Each fix updated the lines its own change made false. This catches what they left.

• User guide: Carve asks only when a carver cuts something ([Build] Check Carve for an overlap before asking to confirm #1267); Ctrl+Z after Save Linked unlinks the selection and keeps the file ([Prefabs] Record an undo step for Save as Live-Linked Prefab #1276); a bake cut short by a scene tab switch stops with a message and keeps its dirty tags ([Bake] Survive a scene tab switch in the middle of a bake #1290); the spawn's angle turns however the spawn is turned ([Objects] Turn a spawn's angle when it is turned with the gizmo or the Inspector #1285).
• DEVELOPMENT: a "Commands" bullet says where a palette command lives (its HFCommandRegistry entry and its execute() arm) and what catches a missing half. The hf_keymap.gd module line no longer claims five categories; labels and categories come from the registry.
• SPEC: Customizable Keymaps says labels and categories come from HFCommandRegistry.
• Smoke checklist: three real-editor steps the headless tests cannot reach: a door and a spawn turned with Godot's gizmo ([Objects] Turn a door's angle when its brushes are turned with the gizmo or the bridge #1256, [Objects] Turn a spawn's angle when it is turned with the gizmo or the Inspector #1285), Carve on a box that overlaps nothing ([Build] Check Carve for an overlap before asking to confirm #1267), and a Test Level bake cut short by a tab switch or by turning the plugin off ([Bake] Survive a scene tab switch in the middle of a bake #1290, [Test] Stop a baking dock action quietly when the plugin is disabled mid-bake #1288).
• Doc comments: HFCommandRegistry.has() and needs_level(), HFMcpCommands.params_schema(), and a note above the check_<form> functions on what each answers.
• tests/test_undo_sweep.gd: an assertion message still said the actions came from plugin_commands.gd; they come from the registry.

The changelog line is a fragment. The compile of today's earlier fragments is its own PR (#1292).