Add runtime version source and exposure

[stef-k]

Summary

• Fixes Define single source of truth for Wayfarer runtime and release version #322.
• Adds Version.props as the runtime version source with WayfarerVersion set to 1.4.0.
• Exposes the compiled version through dotnet run --no-launch-profile -- version, GET /api/version, X-Wayfarer-Version, and the shared layout footer.
• Keeps release-helper automation, changelog checks, tag validation, and GitHub release validation deferred to Add release helper automation for Wayfarer version bumps #324.

Validation

• dotnet build - passed, 0 warnings/errors.
• dotnet test --filter Versioning - passed, 10 tests.
• dotnet run --no-launch-profile -- version - output exactly Wayfarer 1.4.0.
• dotnet test - passed, 1595 tests.
• dotnet run --project tools/Wayfarer.LocCheck -- --warn 400 --fail 600 - passed; warnings are existing Trip Editor/legacy LOC warnings, not files changed by Define single source of truth for Wayfarer runtime and release version #322.
• git diff --check origin/main...HEAD - passed.

Notes

• Final read-only review passed against origin/main...HEAD; local main was stale and was not used as the review base.