fix(templates): stop the panel grid overflowing below 336px

[scheemunai]

The defect

metrics-dashboard scrolls sideways at narrow widths. Reproduced locally and matching the production measurement exactly:

320 -> 16px overflow
328 ->  8px
336 ->  0

An auto-fit minmax floor wider than the content box cannot shrink, so the grid item overflows the page rather than the track collapsing. .panels used minmax(20rem,1fr) — 320px inside a 288px content box.

- grid-template-columns:repeat(auto-fit,minmax(20rem,1fr))
+ grid-template-columns:repeat(auto-fit,minmax(min(20rem,100%),1fr))

Scope: one live, five preventive

Guarded every auto-fit floor ≥14rem across the seven research and status templates. Swept all seven from main at every width 320–420:

template	on main
metrics-dashboard	overflows, 320–335
the other six	clean

So only one is live. The other five floors are narrower than the box at present and depend on padding and content not changing — they are guarded because it is the same defect and the fix is one line each, not because they fail today.

Height-neutral, verified rather than assumed

Swept 320–1920 before and after:

	main	guarded
report · research-brief · postmortem · case-study · project-status · service-health	—	identical peaks
metrics-dashboard	2573 @320	2601 @320

The one change is real and expected: content that was spilling sideways now wraps inside the viewport, so 28px of genuine panel height appears. It was previously hidden by the defect it is being measured against. I would rather report that than claim height-neutrality that is true of six sevenths.

Deliberately carries no height work

Horizontal overflow is a defect at any threshold — nobody chooses to scroll sideways. This is split out of #30 so the one-line fix does not wait on the 2,900 re-derivation. #30 is parked, not abandoned.

Verified with builder-1's width-sweep.cjs, which asserts innerWidth before every recorded value and refuses rather than records, and reports overflow as a first-class failure — which is the only reason this was findable at all, since metrics-dashboard passes every height check comfortably.

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