chore: release githits and MCP 0.20.0

[jlitola]

Prepare githits@0.20.0 and @githits/mcp@0.20.0 from main at 27f57d4, including #401, #402, #403, and #405. Both artifacts require a minor bump because #402 replaces three MCP package-coordinate inputs with one required canonical target on four tools.

• Migrate MCP docs_list, pkg_info, pkg_vulns, and pkg_deps calls from registry, package_name, and version to target; pkg_info now requires an unpinned target. CLI syntax remains unchanged.
• Include compact agent instructions, stable hosted-documentation follow-ups, and internal agent-eval improvements from the remaining pending fragments.
• Consolidate all five fragments into separate package changelog sections. Align package, lockfile, MCP registry, and generated plugin versions.
• MCP clients must refresh tool discovery and migrate the four changed call shapes. Hosted rollout also requires remote-mcp to adopt and deploy the new MCP package.

Validation:

• bun test: 4,826 pass, 0 fail, 17,131 assertions.
• Typecheck, formatting, lint (8 existing warnings), build, plugin generation/check, and diff checks pass.
• Public package validation and the MCP publish dry run pass.
• Source CLI smoke passes 116 stable/experimental live steps; source MCP smoke passes 61 stable/experimental live steps.
• Built CLI smoke passes 31 unauthenticated steps; built MCP smoke passes 9 registration steps.

Validation limit:

• The pinned mcp-publisher used by release CI is not installed locally, so standalone mcp-publisher validate server.json was not rerun. Repository registry-manifest tests and package validation pass.

Release preparation only. Merge requires explicit human approval for this PR; auto-merge is disabled.