polish: S6 personalization — subtler voice injection + flexible video prompts

[0b00101111]

Problem

S6 over-applies vocabulary (every sentence gets "no cap" and "lowkey") and generates over-specified video prompts (shot-by-shot storyboards for 28-second TikToks). Real creators use catchphrases selectively and work from loose concepts, not film scripts.

Suggested Improvements

1. Instruct catchphrase use sparingly (max 2-3 per script, at emphasis points only)
2. Offer two video prompt formats:
   • "quick concept" (3-5 lines for experienced creators)
   • "detailed brief" (full breakdown for production teams)
3. Cross-reference with creator's recent output to avoid repeating topics/hooks
4. Expand CreatorProfile to include speaking rhythm and storytelling style (see polish: expand CreatorProfile model #52)

Context

See design/pipeline-quality-review.md

Depends on

• PR feat: dataset prep + first real pipeline run (M1-6) #49 (M1-6)
• CreatorProfile expansion