26.4.2

Fix Docker image + enable MCP Registry publishing

What changed

• docker/Dockerfile — switched from a custom adduser step to USER $APP_UID, the non-root user pre-shipped by mcr.microsoft.com/dotnet/aspnet:10.0 (UID 1654). The previous adduser command was Debian-specific and broke on the Azure Linux base image that Microsoft now uses for .NET 10.
• src/GroupDocs.Metadata.Mcp/.mcp/server.json — shortened description to fit the MCP schema's 100-character cap and dropped inaccurate "write" wording (the server only exposes ReadMetadata and RemoveMetadata, no write tool).
• .github/workflows/run_tests.yml — replaced the ajv-cli schema-validation step with check-jsonschema, which handles the MCP schema's cross-draft $ref to the draft-07 meta-schema natively instead of tripping ajv's strict mode.
• MCP Registry publishing enabled — MCP_REGISTRY_PUBLISH=true repo variable now set, so publish_prod.yml → publish_mcp_registry runs on every release via GitHub OIDC.

Why

The 26.4.1 release succeeded on NuGet but the Docker image build blew up on the adduser step (Azure Linux base doesn't ship Debian's adduser wrapper), and the MCP Registry step was gated behind an opt-in variable that hadn't been set — so 26.4.1 was never listed at registry.modelcontextprotocol.io. 26.4.2 is the end-to-end verification that all three channels (NuGet + Docker + MCP Registry) publish cleanly from a single release.

Migration / impact

None for consumers. No API changes, no behaviour changes — same two tools, same env vars, same schema.

Full Changelog: 26.4.1...26.4.2