fix: materialize mesh topology updates locally

[LiranCohen]

Summary

• make meshd peer list strictly socket-local and serve the daemon snapshot without DWN fallback latency
• bootstrap one validated raw topology baseline, apply ordered subscription deltas transactionally, and hydrate only missing winning payloads
• use exact DWN write/delete/prune/squash semantics, recipient-aware last-good parsing, and bounded audience-key miss caching
• reserve full reconciliation for startup and repair, with cursor pagination, eight bounded workers, atomic cut fences, and request/record/byte limits
• fail closed for unreadable ACL/relay/self state; publish an expired zero-peer down map for self revocation and reproject peer expiry locally
• bound WebSocket and HTTP response memory, harden queue accounting, and preserve caller ownership for endpoint updates

Closes #260

Validation

• go build ./...
• go vet ./...
• go test ./... -count=1 -race
• git diff --check
• independent production audit: no release blockers

Follow-ups

• fix: serialize and coalesce endpoint publication #261 serializes and coalesces endpoint publication
• feat: subscribe to audience and grant-key control records #262 adds dedicated audience and grant-key streams
• perf: add authorization-tested broad topology query fast path #263 adds an authorization-tested broad-query fast path