Improve Graph search: gold glow, ref matching, guided navigation

[danipen]

Summary

Reworks the Graph tab's search into a text-editor "find" experience on canvas: every hit glows warm gold, the current hit wears a wider corona and lands with a brief sonar ping, and stepping (Enter / arrows) walks the results newest-first.

• Typed search hits. Search now matches commits and branch labels and tag chips. Searching a ref name finds the ref itself — its pill/chip lights up and is what Enter steps to — never the commit it happens to decorate. Pure logic lives in the new, directly-tested searchGlow.ts (computeSearchHits, pingRings, withAlpha, litChains).
• More visible results. Hits glow gold with a per-hit corona; the active hit gets a wider "you are here" glow and an arrival ping (two staggered rings that expand and fade).
• Ghost the rest. Non-matching commits, branch labels of chains with no hit, and the uncommitted node all dim/ghost so a lit element never claims a match it doesn't have.

Testing

• bun run lint ✅
• bun run typecheck ✅
• bun test ✅ (adds searchGlow.test.ts)