[cbaucom]

Closes #10

Summary

• Adds three theme presets as pure data (THEMES record in timeline-core/settings.ts): Classic (crossfade, Ken Burns, 4s), Energetic (cut, Ken Burns zoom-in-only, 2s), Plain (cut, no Ken Burns, 5s)
• kenBurnsMode?: 'alternate' | 'zoom-in-only' added to GlobalSettings; planner selects zoom-in-only KB presets when set
• applyTheme(name) returns a fresh copy of the theme settings
• Theme selector UI (3 buttons) in GlobalSettingsPanel; active theme highlighted; manual settings edit clears active selection
• themeName persisted in slideshow.json and restored on project open

Acceptance criteria

• Given each theme applied, when played, then global behavior matches its definition — verified by unit tests on THEMES presets (transition type, Ken Burns, pacing) and by Playwright smoke check confirming settings panel updates correctly
• Switching themes is non-destructive to per-slide overrides — themes only replace globalSettings; per-slide overrides are untouched
• Given Plain theme, when played, then there are zero transitions and zero motion, images hold exactly the configured duration, and videos play as-is — THEMES.plain = { transitionType: 'cut', kenBurns: false, imageDurationSecs: 5 }; verified by unit test and planner behavior; HITL aesthetics sign-off required before merge
• HITL: owner reviews each theme on a real photo/video set and signs off on aesthetics

Approach

Themes are purely data — no special-cased code paths. A theme is a GlobalSettings object; applying one calls setGlobalSettings(applyTheme(name)) (full replacement, not merge), so no stale fields survive a theme switch. kenBurnsMode flows through the existing resolve() cascade.

Code review verdict

APPROVE — zero blocking findings from --effort high review. Both candidate concerns (stale kenBurnsMode on theme switch, invalid themeName crash on load) were REFUTED: theme application does a full state replacement, and applyTheme is never called during project load.

Screenshot

Theme selector visible in settings panel; Energetic active (blue highlight), Transition = Cut, Duration = 2s:

Follow-ups noted

• No UI control to set kenBurnsMode independently of themes (zoom-in-only is only reachable via Energetic theme); fine for v1 since it's an aesthetic preference