fix(store): fence concurrent record reads

[nstranquist]

Summary

• preserve complete typed error and recovery data for concurrent capture failures
• stress 25 exact shared-lane capture iterations on each Windows CI job
• serialize operational lane and lease reads with atomic record replacement
• serialize the final durable commit receipt through the same registry fence
• retain every source HEAD, index, path-isolation, ref, and intent assertion

Root cause

Hosted attempt 3 reproduced STORE_FAILED while Current/Status opened a lease record during another lane heartbeat replacement:
https://github.com/nstranquist/wip-commit/actions/runs/32035869370/attempts/3

Unix permits the rename window. Windows can reject the open with a sharing violation. The registry fence now covers both sides of that operation.

Verification

• deterministic tests prove operational reads and RecordCommit wait for the registry fence
• 100 local exact concurrency iterations passed
• go test -count=1 ./...
• go test -race -count=3 ./...
• go vet ./...
• actionlint
• golangci-lint run ./...
• gitleaks history and worktree scans
• both initial hosted Windows jobs passed on the fixed head

Refs #6.

[nstranquist]

Windows stress attempt 3 reproduced the original failure with typed evidence: STORE_FAILED while Current/Status opened a lease record during another lane heartbeat atomic replacement. The operational reads and RecordCommit now use the same registry fence as lease replacement (11e1915), with deterministic fence tests plus 100 local concurrent capture iterations. Hosted Windows verification is running on the fix.