surf suggest: propose anchors from public symbols (lower authoring cost)

[Connorrmcd6]

Why

Surface's main adoption cost is authoring claims/anchors by hand (§8). drift's zero-config "point it at the repo and go" is much lower friction. We can borrow the spirit without giving up explicit anchors.

What

surf suggest (or surf init --scan): scan public/exported symbols (and high-churn files) and propose candidate anchors / a starter hub the author can edit and verify. Suggestions only — never auto-stamps.

Notes

• Reuse collect_all_defs (surf-core/src/resolve.rs) to enumerate symbols.
• Heuristics for "worth anchoring" tie into lint: granularity guidance (over/under-anchoring) #6 (granularity guidance).