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.

docs/ui-copy.md

@@ -1,6 +1,6 @@
 # UI copy and button inventory
 
-Status: dialogue pass complete; button/focus/font-scale audit in progress for 0.9.3.
+Status: dialogue and button-state passes complete; focus/layout audit in progress for 0.9.3.
 
 ## Screen inventory
 
@@ -90,6 +90,25 @@ silent profiles can still return an empty context line.
 | Repetition | Shared tourist/confused/delivery lines recur across venues by design; role-specific reason lines prevent every archetype sounding alike. | Accepted for the shared-archetype model. |
 | Localization length | Longest authored NPC/door line is 56 characters; longest UI string is `hud.controls` at 172 characters. | Dialogue fits the HUD log; the 1.5–2× string/font-scale layout test remains a separate 0.9.3 task. |
 
+## Button state audit
+
+All `Button` controls now use `src/game/ui/ui_styles.gd`, which defines explicit
+**normal**, **hover**, **pressed**, **focus** and **disabled** styles plus the
+matching font colours. This removes the engine-theme fallback that previously
+appeared when a custom dark button was disabled or focused by keyboard.
+
+| Surface | States / behavior checked | Result |
+| --- | --- | --- |
+| Start menu | Venue rows, Continue, Help, Settings, Quit; focus clamped to the list; Continue hidden when the campaign is complete. | All buttons styled; hidden state is intentional, not a disabled state. |
+| Tutorial | F1 skip is a keyboard shortcut, not a button; its hint is non-interactive. | Keyboard-only by design; no hover/focus state to style. |
+| Pause | Resume, Restart, Settings, Quit to menu; Resume receives focus on open. | All four states styled; focus is distinct from hover. |
+| Settings | Replay tutorial, Reset campaign, key-binding rows, Apply settings, Cancel; rebinding shows “Press…” while listening. | All action buttons styled; reset-confirmation dialog OK/Cancel styled; fields keep the engine control theme. |
+| Help | Close; Esc still closes. | Styled; no disabled state is used. |
+| Shift review | Continue campaign, Body camera timeline, Return to menu, Quit game; Continue hidden when the campaign is complete. | All styled; hidden state is intentional. |
+| Timeline | Previous/Next/Close; Previous is disabled at the first event, Next at the last, and both when empty. | Disabled state verified in `test_event_timeline.gd`; Close stays enabled. |
+| Radio | Send request, Send emergency, Cancel. Emergency hold uses press/release, so the action button stays enabled while holding. | All styled; disabling it during the hold would break confirmation. |
+| Toggles | CheckButton/OptionButton controls keep the engine theme. | Intentional: the shared style targets action buttons, not checkbox/radio affordances. |
+
 ## Remaining audit work
 
 - Player-facing labels are now routed through `content/strings.en.json`; numeric