v0.26.0

• Add timer: start, timer: pause, and timer: resume slide metadata, applied when advancing away from a slide in the presenter or display.
• Normalize slide durations to finite, non-negative floating-point seconds. Missing or invalid durations now default to 0.0, and negative durations are clamped to zero. Presentations relying on the previous 60-second default should set explicit durations.
• Handle zero-duration slide progress and hide pacing indicators, progress, and remaining-time estimates when a presentation has no allocated duration.
• Keep recorder navigation from changing the presentation timer.