Normalize build and CI/CD; add lineeditor router

[uniblab]

Normalize Icod.LineEditor to the canonical uniblab/.github C#/.NET build and release pattern and add a distribution router for the command suite.

Router

• add Icod.LineEditor.Router with assembly/executable name lineeditor;
• expose lineeditor ed, lineeditor red, and lineeditor sed in-process dispatch;
• retain standalone ed, red, and sed executables;
• add router help/version/dispatch tests;
• add the router and its tests to Icod.LineEditor.sln;
• package the router as Icod.LineEditor.Tools with installed command lineeditor.

Build / CI normalization

• local wrappers use Debug and clean → restore → build → test → pack → validate;
• add metadata-driven solution/project/executable discovery with repository-relative solution handoff;
• pull requests use Staging on Windows/Linux/macOS with Linux package verification;
• main uses six-runner Release distribution validation on x64 and ARM64;
• add manually dispatched distribution validation;
• add canonical tag release graph with exact tag-version package selection, six RID archives, NuGet/GitHub Packages publication, checksums, and GitHub Release creation;
• remove legacy pr-build-and-test.yaml and push-main.yaml workflows.

Release archives discover executables from MSBuild and include lineeditor, ed, red, and sed together with repository README/LICENSE. Existing product semantics and dependency versions are otherwise unchanged.