feat: add --timeout flag to image, text, and video commands

[Railly]

Summary

Adds a --timeout <seconds> flag to image, text, and video. Defaults are unchanged (120s for image/text, 300s for video), so this is purely additive.

Why

The hardcoded 120s default in image (and text) aborts complex prompts before the AI Gateway has a chance to respond. Real example: a sprite atlas prompt (1536x1872, 72 cells, strict layout constraints) consistently hits the 120s wall and surfaces as Gateway request failed: The operation timed out regardless of model. There is no escape hatch in the current CLI: the user has to fork or downgrade the prompt.

The Gateway itself is not the bottleneck. Per AI Gateway docs, provider timeouts go from 1s up to 789,000ms (~13 min), and that timeout only measures time-to-first-byte. The CLI's AbortSignal.timeout(120_000) is what fires first.

The current docs even acknowledge this in troubleshooting.mdx ("If you're consistently hitting timeouts, try a faster model variant"), but switching models is not always the right answer — for image generation, model choice is dictated by quality requirements, not latency tolerance.

What changes

• --timeout <seconds> on image, text, video. Reused parsePositiveInt for validation.
• README, commands.mdx, troubleshooting.mdx updated to document the flag and renamed the existing column to "Default timeout" for clarity.
• No default changed, no behavior change for existing invocations.

Verification

• bun run typecheck passes
• bun run format:check passes
• bun run lint passes (24 preexisting warnings, 0 new)
• bun run build produces a working binary
• dist/ai image --help shows the new flag with the correct default

Example

ai image "complex sprite atlas with 72 cells..." --timeout 600
ai text "long structured response..." --timeout 300
ai video "extended scene..." --timeout 900

[vercel]

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[ctate]

@Railly Good one. Can you plz fix the conflict and sign your commit(s) before merging?

[Railly]

@ctate done!