Unify action-button states across the UI

- Add UiStyles with explicit normal, hover, pressed, focus and disabled styles and apply it to every action button.
- Disable timeline Previous/Next at the first/last event and keep Close always available.
- Style settings reset-dialog buttons and cover the button-state audit in docs/ui-copy.md.
- Add shared-state and timeline-boundary regression tests.

MEMORY.md

@@ -61,6 +61,10 @@ Session memory for durable decisions, state, and gotchas. Keep concise, remove o
   gallery is 13 good / 0 bad, the screen-design judge is 13/13 and a clean
   portrait measured a 0.732 vision gap against the photoreal concept. No
   release build, version bump or tag was created at this gate.
+- **Button states (2026-11-02):** `src/game/ui/ui_styles.gd` owns the five action-button
+  states and font colours for the dark session/UI shell. Use `UiStyles.apply_button()`
+  for every new `Button`; CheckButton/OptionButton keep the engine theme. Timeline
+  Previous/Next disable at the ends; F1 tutorial skip is keyboard-only by design.
 - **Version and roadmap renumber (2026-11-02):** source is now **0.9.2**; the
   completed map/NPC work is the patch content. Postponed work is renumbered to
   **0.9.3 UI**, **0.9.4 NPC**, **0.9.5 textures**, **0.9.6 integration**, then the
@@ -702,7 +706,7 @@ Session memory for durable decisions, state, and gotchas. Keep concise, remove o
 - Venue `door_staff_lines` are logged through `GameManager` (inspect / wand / refuse). They are not a separate dialogue UI.
 - Access loadout is implemented; do not re-fix `override_access` as if it were still unread.
 - `Save.SETTINGS_FILE` is declared and unused; settings persistence goes through `Save.load_settings()` / `save_settings()`.
-- Headless suite is **258/258**; the windowed smokes, screenshot compare and judge pass. Remaining visual follow-ups are in `TODO.md`.
+- Headless suite is **259/259**; the windowed smokes, screenshot compare and judge pass. Remaining visual follow-ups are in `TODO.md`.
 - Typed spawn signal extra args: handlers must accept the 4th `event: Dictionary` or Godot will not call them (`test_shift_coordinator_runs_a_shift` failed until `_on_spawn` took four args).
 - GDScript inference trap that broke the main scene: a `var` typed as a base class
   (`radial: CanvasLayer`) exposes script members as `Variant`, so `var x := radial.is_open` is a