[foxnne]

Part of fizzyedit/work#16

What changes

• A demo caption stays up Script.reading_ms_per_word (300 ms) per word of title and text at 1x, never under Script.reading_min_ms (2 s). Both are named constants. The old character-count formula with its 12 s cap is gone, so long captions no longer vanish quickly.
• Playback speed moves from Player.rate into Sequencer.speed: a plain f32, default 1, clamped to 0.5..4 (setSpeed), stepped through Sequencer.speeds = 0.5, 0.75, 1, 1.5, 2, 3, 4 (stepSpeed). playUntil turns a frame's wall time into demo time and wallMs divides a caption's ms by speed, so the whole demo speeds up with it.
• Seek and rewind ask advance for a demo time, which no speed enters, so they stay exact at any speed.
• The 0.25x notch is dropped (the floor is 0.5). Player.rate/setRate/stepRate are replaced by player.seq.speed/setSpeed/stepSpeed; the overlay, Editor.zig and the demo.speed command follow. No UI added; the slider is a later PR.
• docs/AUTOMATION.md describes both.

Verification (Linux cloud)

• Unit tests: word counts, the 2 s floor and its boundary, title plus text; every notch (0.5 to 4) through playUntil/wallMs; clamping and stepping; a rewind and replay lands on the same moment at every speed.
• Gates: scripts/check-fmt.sh, scripts/zb build, build test, build test-integration (92/92 steps succeeded), build check-web, build test-sdk-version, build lint, build check-tests-reached all pass.
• Not seen in a running app: no UI change besides the speed label reading seq.speed.
• The SDK fingerprint did not move; sdk_version untouched.

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Generated by Claude Code