Retire .Core from the published package ID

[matt-edmondson]

TUI.Core.csproj publishes as ktsu.TUI.Core. It should publish as ktsu.TUI.

Whether a repo splits its library into a .Core project is an internal decision about whether it
also ships an executable. Because the package ID mirrors the project name, that decision is
published. Forty-odd single-library repos in the org publish under the bare family name, so
consumers write ktsu.Extensions and ktsu.Containers but ktsu.TUI.Core here.

This one is live on nuget.org, so it is genuinely breaking rather than free.

Current package ID	ktsu.TUI.Core
Versions published	58, latest 1.0.47
Target	ktsu.TUI

Convention

A repo's principal package is ktsu.<Family>, where <Family> is the repo name, the solution
filename, and the leading segment of every package in the repo. The project filename is the package
ID minus ktsu.. Assembly name and root namespace equal the package ID.

Change

1. Rename TUI.Core to TUI (folder, .csproj, and the solution entry).
2. Ship ktsu.TUI at the next major.
3. Republish ktsu.TUI.Core once as a deprecated meta-package that depends on ktsu.TUI, so pinned
   consumers get a working upgrade path rather than a dead ID.

Also in this repo, and free

TUI.CLI should be TUI.Cli. The convention uses PascalCase segments throughout, so an
all-caps CLI is the outlier. ktsu.TUI.CLI is not on nuget.org (the project is OutputType=Exe,
so ktsu.Sdk leaves it unpackable), so this rename costs nothing. TUI.App already matches.

If not now

Defer indefinitely if consumer churn outweighs the consistency. Nothing else in the audit depends
on this step. The rest of the naming work in this repo is free and can land without it.

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Part of the estate-wide naming audit tracked in ktsu-dev/Sdk#36.