refactor(stern) revert LinkRaw / BulletinRaw to positional records

[jkeeley2073]

Summary

Closes docs/build-spec.md Phase 2 § Scope item 6 (Wave 2).

The package bump itself already landed in PR #61 (commit 43c1f23, feat(deps) bump all NuGet packages to latest stable) — Microsoft.Playwright is at 1.59.0. The remaining work for this scope item was the records-workaround revert from PR #34: convert LinkRaw / BulletinRaw (class-with-init-properties workaround for Playwright 1.12.0) back to positional records, since Playwright 1.59.0 deserializes via System.Text.Json which supports records natively.

The build-spec entry has been corrected to reflect this reality.

Background

PR #34 (Oct 2025) converted these records to classes because Playwright 1.12.0 used Activator.CreateInstance(type) to materialize JS-evaluation results — that call fails on positional records (no parameterless ctor). Playwright 1.59.0 uses System.Text.Json instead, which supports positional records natively via the synthesized constructor.

What ships

• LinkRaw and BulletinRaw revert from class-with-init-properties to positional records with [property: JsonPropertyName] attributes
• Href is string? (not string): matches the System.Text.Json contract on missing fields (STJ assigns null, not empty string, when a property is absent). The downstream IsNullOrWhiteSpace guards already coalesce null and empty, so behavior is preserved; the type now honestly reflects the runtime nullability the deserializer enforces
• Both records change from private to internal so the new SternPlaywrightRecordDeserializationTests in the test assembly can pin the contract
• PinballWizard.Infrastructure.csproj adds [InternalsVisibleTo] for PinballWizard.Scraper.Tests with a comment explaining why (Stern Playwright scrapers have no automated integration tests per Phase 2 § Scope item 8 route ii; live-site validation is the only other check, and a JsonPropertyName typo would only surface as "0 results discovered" in production)
• 6 new tests in SternPlaywrightRecordDeserializationTests pin: full-payload deserialization (both records), optional fields omitted → null, required field (Href) omitted → null (matching the downstream guards' contract)
• docs/build-spec.md Phase 2 § Scope item 6 updated to reflect reality

Test Plan

• dotnet test PinballWizard.slnx --nologo → 524 / 524 passing (was 518; +6 deserialization tests)
• dotnet build PinballWizard.slnx --nologo → clean, zero warnings
• The new tests deliberately exercise the same path Playwright invokes (System.Text.Json against the record types). A JsonPropertyName typo or breaking change to STJ's record handling fails these tests at build time, not at "0 results" against the live site

Local review

/local-review outcome: 0 🔴 / 2 ⚠️ / 8 categories ✅.

• ⚠️ Fixed — Href: string → string?: matches the System.Text.Json contract on missing fields. Downstream guards unchanged; type is now honest.
• ⚠️ Fixed — added SternPlaywrightRecordDeserializationTests (6 cases) to pin the contract Playwright invokes.

Operational hand-off after merge

• Run dotnet run --project src/PinballWizard.Cli -- --source games and --source bulletins against sternpinball.com and confirm the scrapers still produce non-zero ScrapedItem yields with full provenance. The new tests pin the JSON contract; the live-site validation pins the end-to-end Playwright integration.
• If the live-site validation surfaces a regression, revert this commit and document why classes are still required (the comment in the file already references the historical PR fix(scrapers) wire JJP machine filter, harden Spooky, add pre-push self-audit #34 reasoning).

7-item self-audit

1. Every option field is read — N/A (no options)
2. Sibling-diff — LinkRaw and BulletinRaw are now syntactically identical (positional records, [property: JsonPropertyName], string? for Href, comments cross-reference each other consistently)
3. No bare catch { } — pre-existing bare catches in ClickTabAsync / TryClickLoadMoreAsync are NOT introduced by this PR (out of scope)
4. CLI / orchestrator wiring — no CLI changes; tests pin the deserialization that the existing --source games / --source bulletins paths invoke
5. Tests assert behavior — the 6 new tests deliberately use real System.Text.Json against real record types, with full / partial / missing-required payloads
6. Build is zero-warning — verified
7. Identity check — git log -1 --format='%an <%ae>' → Jim Keeley <94459922+jkeeley2073@users.noreply.github.com> ✅

Out of Scope

• Item 6 operational hand-off — happens after merge as a small ops task (live-site validation against sternpinball.com)
• Item 7 round 2 (Dependabot bumps chore(deps)(deps): bump actions/cache from 4 to 5 #5–chore(deps)(deps): bump actions/upload-artifact from 4 to 7 #9) — separate; can be merged in any order, no code change

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