feat: model menu keyboard machine + graph center-anchor on resize

Owner polish pair before the settings milestone:

- Model menu: arrows walk the filtered results (clamped, no wrap) while
  focus stays in the search field; Enter picks the walked row or, with no
  walk yet, the first result; typing resets the walk; click and Enter
  share one pickModel path; walked row gets a muted ring + scrollIntoView;
  cheat-sheet display entries added.

- Graph: window resizes re-anchor the camera so the world point under the
  pre-resize viewport center stays under the new center — the graph stays
  visually still while scaling (was top-left pinned). viewW/H tracked in
  syncSize; re-anchor applied through the zoom behavior (persistence and
  card-dismiss unchanged); kFit refresh as before. Pixel-verified: 7/7
  center samples identical across a 300x200 shrink.

docs/research/graph-rendering.md

@@ -225,3 +225,17 @@ LinLog-only FA2 (one afternoon), then the two-level pipeline
   (geometry already unit-tested in `components/cluster-geometry.ts`).
 - Label-gate hysteresis: small dead-band in log-zoom to avoid threshold flicker.
 - Whether layout runs server-side at extraction (persisted as data) or in-browser.
+
+## Center-anchor on window resize (2026-09-17)
+
+The camera translate is measured from the canvas's TOP-LEFT corner, so a
+window resize used to keep the top-left pinned and the graph appeared to
+slide by half the size delta (owner report). The resize observer now
+captures the world point under the PRE-resize viewport center (from the
+last-synced `viewW/H` — the ResizeObserver already sees the new size in
+clientWidth/Height), then re-anchors the translate so that same world
+point lands under the NEW center (applied through the zoom behavior, so
+d3 state, camera persistence, and card-dismiss all behave like any
+camera move). Zoom (k) is untouched; `refreshFitZoom` metadata is
+viewport-bound and recomputed as before. Verified by canvas pixel
+sampling: 7/7 center-area samples identical across a 300×200 shrink.