Stabilize release tests on current Go toolchains

[darron]

What changed

• Warm the lazy link-capture admission SQLite pool before measuring semantic-lease independence. The test now measures lock behavior instead of one-time connection setup.
• Update github.com/go-json-experiment/json to a revision compatible with the JSON v2 APIs exposed by Go 1.27 (json.SkipFunc and json.DiscardUnknownMembers).

Why

The release test intermittently failed because the first admission-pool connection could take just over the test's 200 ms timing threshold while an unrelated semantic lease was held. Separately, local Go 1.27 builds failed before tests compiled because the old indirect JSON module referenced standard-library APIs that are no longer present under that toolchain.

Verification

• go test -race ./internal/store -run '^TestLinkCaptureQueueDoesNotWaitForSemanticLease$' -count=100
• go test -race ./internal/store -count=1
• go test -mod=readonly -race ./internal/store ./internal/mediadownload -count=1
• Full task test-ci under Go 1.27.0
• CI-pinned golangci-lint v2.12.2: 0 issues

The release retry also completed the Verify job and the linux/amd64, linux/arm64, darwin/amd64, and windows/amd64 builds successfully while this PR was prepared; the native darwin/arm64 build was still running at the last check.

[github-actions]

PR Diff Stats

PR #171 changed 4 file(s), with +21 / -3 (24 changed lines).

Bucket	Files	Additions	Deletions	Changed
Docs	1	+8	-0	8
Tests	1	+10	-0	10
Migrations	0	+0	-0	0
Generated	0	+0	-0	0
Lockfiles	1	+2	-2	4
Config / Ops	0	+0	-0	0
Code	1	+1	-1	2
Total	4	+21	-3	24

Largest Changed Files

File	Bucket	Additions	Deletions	Changed
internal/store/link_capture_test.go	Tests	+10	-0	10
CHANGELOG.md	Docs	+8	-0	8
go.sum	Lockfiles	+2	-2	4
go.mod	Code	+1	-1	2

Bucket rules

• Docs: Markdown/text docs such as docs/**, README.md, and other *.md or *.txt files
• Tests: *_test.go, test/, tests/, e2e/, and JS/TS *.test.* or *.spec.* files
• Migrations: schema migration/init files such as internal/store/migrations.go and internal/store/schema_init.go
• Generated: local runtime/generated surfaces such as data/, logs/, tmp/, vault/, and web/ui/dist/
• Lockfiles: dependency lockfiles such as go.sum and package-lock.json
• Config / Ops: CI, config, packaging, skills, deploy, and scripting files such as .github/, packaging/, skills/, scripts/, Makefile, Dockerfile, Taskfile.yml, config.yaml.sample, and fly.toml
• Code: everything else