feat(lint): warn when a class="clip" element partially overrides inset:0

[miguel-heygen]

Root cause

The canonical .clip rule (see hyperframes-core/minimal-composition.md) is position: absolute; inset: 0, so every class="clip" element is pinned to all four edges by default. A more specific selector (an #id/.class <style> rule, or an inline style) that overrides only some of top/right/bottom/left without also giving width/height leaves the un-overridden sides pinned at the base 0 — so the element silently stretches between the author's sides and the inherited zeros instead of shrink-wrapping to its content.

Reported four independent times (e.g. a user sets bottom: 40px; left: 40px expecting a corner-anchored box and gets a full-screen stretch). inspect catches the symptom (content_overlap / text_occluded) but never names the CSS root cause, so each reporter had to getBoundingClientRect()-probe to diagnose it — and several asked directly for exactly this lint rule.

The rule (clip_partial_inset_stretch, warning)

• Self-gating: only fires once the file's own .clip rule actually establishes the base (position:absolute|fixed + all-zero inset). Compositions that define .clip differently never trip it.
• Per class="clip" element, merges its override declarations — matching #id/.class <style> rules by their selector subject (rightmost compound), plus inline style; the bare .clip base rule is excluded since it's the inherited pin, not an override — and flags an axis only when the author pinned exactly one of that axis's two sides with no size for the axis.
• That "exactly one" gate is what keeps intentional shapes quiet: full-bleed (0 sides set), fully-constrained 4-side boxes, sized boxes (width+height), and position:relative/static/sticky all stay silent; auto on the opposite side (an explicit release of the base pin) also silences it.

High-precision by design. inspect remains the runtime backstop, so the rule deliberately under-reports (exotic/compound selectors, @media-nested overrides) rather than risk false positives on the lint path that runs constantly.

Test plan

• 9 end-to-end cases via lintHyperframeHtml: bottom+left corner / single-side / inline-override → flag; sized box / full-bleed / all-four-sides / auto-release / position:relative / no-base → quiet.
• 7 direct unit tests of the pure box-model helpers (collectClipBoxProps / clipStretchAxes) covering the XOR gate, inset shorthand, auto-release, position-detach, and declaration-block ordering (later wins).
• Full lint package suite passes; applyDecl refactored to a dispatch table so fallow's complexity gate passes cleanly (no suppression).
• bun run build clean; oxlint/oxfmt clean.