fix: honor playback speed settings in embeds

[richiemcilroy]

Embedded videos now use the same default playback speed as share links: the video setting takes precedence, then the organisation setting, then Cap’s existing 1.2× fallback. This fixes embeds starting at 1.2× after an organisation has selected 1×, across MP4, HLS, and minimal embeds.

Validation: 69 focused tests pass across embed speed, playback/branding, oEmbed, Player.js, and share-page loading. Biome and scoped TypeScript checks pass for all four changed files. The new client regression cases failed before the fix. Browser playback has not been replayed; the shared local web runtime is in use by another task.

Confidence Score: 5/5

The PR appears safe to merge, with playback-speed resolution and propagation consistently implemented across embed variants.

Summary

• Resolves the effective default speed on the embed server page.
• Propagates that speed through both MP4 and HLS player paths, including minimal embeds.
• Adds regression coverage for precedence, invalid and legacy values, source variants, and minimal presentation.

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