feat(cli): flag overlapping text blocks in inspect

[LeopoldTr]

Problem

hyperframes inspect compares each element against its container (overflow, clipping). It never compares two siblings against each other, so two text blocks that collide — each sitting perfectly inside its own box — render unreadable yet the audit stays green. Stacked headings, a caption landing on a title, two labels animating into the same spot: all invisible to the current checks.

Solution

Add a content_overlap check. After the overflow passes, it collects the solid text blocks (visible, text-bearing, not watermark-faint) and reports any pair whose text boxes intersect by more than a fifth of the smaller box. The finding names both blocks (selector + containerSelector), is rated error (same as clipped_text — both make text unreadable), and carries a fix hint.

Exemptions keep it quiet on intentional design:

• Watermark-style text (colour alpha < 0.35) is decorative and skipped.
• Nested text (one block inside the other) is never a collision.
• Opt out of deliberate stacking with data-layout-allow-overlap, mirroring the existing data-layout-allow-overflow / data-layout-ignore escape hatches (documented in docs/packages/cli.mdx).

The check reuses the audit's existing visibility, text-rect, and selector helpers, and runs alongside the overflow passes in __hyperframesLayoutAudit — no extra Chrome launch or timeline pass.

Testing

• New unit tests in layout-audit.browser.test.ts: flags two overlapping blocks (asserts both selectors), ignores sub-threshold overlap, ignores low-alpha watermark text, and respects the opt-out.
• Full @hyperframes/cli suite green (771 tests); typecheck, oxlint, oxfmt, and the fallow audit gate all pass.

Note

Independent of #1435 (text occlusion) — both extend the same audit but touch disjoint logic and can land in either order.