fix(region): avoid focus zoom on small filter text

[n30nex]

Opening REGION focuses an 11px input, which can trigger Safari's form-focus zoom and leave the page enlarged after the picker closes. Render that input at 16px at every width. Autofocus, filtering, Escape handling, focus restoration and viewport zoom settings stay unchanged.

Fixes #29.

Validation: build and lint pass (one existing TanStack Virtual warning); all 725 tests pass locally and on the native Pi build. GitHub Actions build passes. The real-browser check in tests/browser/region-input-zoom.js fails on the original 11px input and passes with generated CSS at phone, tablet and desktop widths. Filtering, selection and both Escape actions also pass in the browser.

iOS Safari is unavailable in this test environment, so actual device zoom behavior remains unverified. This PR is independent of the pending header fix #44. Both are combined in the Pi preview at web revision b85bc19a, with matching downloadable source. The public input and header checks pass, and both MQTT feeds continue ingesting.

AI assistance was used for implementation and verification under the author's ongoing contribution workflow.

[n30nex]

@MrAlders0n please review this change with your Claude agent as part of the September 13 Beacon review batch. The current candidate is 77abbac905c6; validation and Pi evidence are in the PR description.

Please check the region input size and preserved focus/filter behavior. An actual iPhone Safari check is especially useful: automated checks verified the 16px input and interaction flow, but do not establish physical-device zoom behavior. Issue #29 is linked for closure on merge.