Tie hero headline display size to word count, not just line count

[codeswithroh]

What this changes

Real skill output ("Flexion," a telehealth product) produced an 8-word hero headline that rendered across 5-6 lines of full-size display type, dominating the hero and crowding the supporting visual next to it. The headline was inside the stated 6-12 word budget, so the word-count rule alone didn't catch this — nothing scaled the type down as the headline got longer, so an 8-word headline at full size simply takes up more vertical space than a 6-word one.

references/hero-guidelines.md:

• Default attention budget — split the 6-12 word range into two size bands: 6-8 words gets the full display size; 9-12 words steps down roughly one clamp tier (~15-20% smaller across the whole clamp() range), not the same size left to wrap across more lines. If a headline needs both the long end of the word budget and the full display size, that's a signal to cut the headline.
• Responsive acceptance checks — added a concrete, checkable condition: at the top of the size range the headline should fit comfortably in 2-3 lines. Wrapping into 5+ lines at full size means step the size down or shorten the headline, not accept it as a width constraint.

Closes #28

Test plan

• Traced the Flexion example against the new rule: at 8 words it falls in the "full display size" band, so the word-count/size split alone wouldn't have blocked it — it's the new acceptance check (2-3 lines at full size, or step down/shorten) that directly catches this case, regardless of which word-count band the headline falls in. Both pieces together are what closes the gap.
• Verified no markdown fence/heading breakage in the edited file