Update to TG 2.5.x (PR 5416 preview)

[tig]

⚠️ DO NOT MERGE with the pre-release pin in place

This PR pins a vendored pre-release build (Terminal.Gui 2.5.0-tig-remove-cm-followup.2, built from tui-cs/Terminal.Gui#5416) so the port can be validated ahead of the v2.5.0 release. Before merging, once a public 2.5.x package is on nuget.org:

1. Update the Terminal.Gui pin to the public 2.5.x version in: mdv.csproj
2. Delete local_packages/ and the tgui-pr-5416 package source in nuget.config (delete the file if that source is all it adds)
3. Revert the .gitignore exception for the vendored packages (if present)
4. Re-run build and tests and confirm Terminal.Gui restores from nuget.org

---

Ports mdv to the Terminal.Gui 2.5.0 preview package as part of the v2.5.0 ecosystem-validation gate (tui-cs/Terminal.Gui#5630). Terminal.Gui PR tui-cs/Terminal.Gui#5416 (ConfigurationManager removal) is not yet merged, so this PR vendors a nupkg built from that PR branch — same pattern as tig/winprint#272.

TEMP: vendored package pin

• local_packages/ carries Terminal.Gui.2.5.0-tig-remove-cm-followup.2 (.nupkg + .snupkg) built from FIXES #4367 - BREAKING CHANGE - Remove legacy ConfigurationManager after MEC migration Terminal.Gui#5416, force-added past the *.nupkg gitignore rule.
• nuget.config adds a tgui-pr-5416 source pointing at ./local_packages.
• mdv.csproj pins Terminal.Gui to 2.5.0-tig-remove-cm-followup.2.

Follow-up: once 2.5.x is published to nuget.org, swap the pin to the public package and delete local_packages/ + the tgui-pr-5416 source.

Code changes (2.5.0 API breaks fixed)

• ConfigurationManager removal — ConfigurationManager.Enable (ConfigLocations.All) is gone in 2.5. Replaced with new TuiConfigurationBuilder ().ApplyToStaticFacades (); library defaults, ~/.tui, ./.tui, and TUI_CONFIG are also applied at assembly load via TuiConfigurationBuilder.Shared.
• TextMateSyntaxHighlighter.GetThemeForBackground is now [Obsolete] (syntax colors resolve from ThemeManager.Theme via VisualRole.Code* roles). Still functional; suppressed CS0618 with a follow-up note to migrate the auto light/dark theme selection.

No other 2.5.0 breaks hit mdv: it does not override View.Text (only assigns it) and does not reference IAcceptTarget, and the repo has no config.json.

Verification

• dotnet build: 0 warnings, 0 errors.
• No test projects in this repo (CI is publish-on-release only).
• Smoke-tested both modes via tuirec (PTY): mdv --print README.md renders the full README with formatting intact; full-screen mdv README.md shows content, StatusBar (Quit / Content Width / Theme / line count), scrolls, and quits cleanly on Esc — the default Quit key from Application.GetDefaultKey (Command.Quit), shown as Esc Quit in the StatusBar. (An earlier revision of this description said Ctrl+Q; Ctrl+Q is not bound — same as rc.3 on main, verified by cast.) No exceptions in either cast.
• Multi-file mode (mdv README.md second.md): File selector dropdown renders in the StatusBar, opens on click, and selecting the second file loads and renders it; clean alt-screen exit on Esc.
• Clean-cache restore verified: with an empty NUGET_PACKAGES, dotnet restore --force resolves Terminal.Gui 2.5.0-tig-remove-cm-followup.2 from the vendored ./local_packages feed.
• Re-vendored to followup.2 (built from 5416 head e8aba423): followup.1 was built from a stale 5416 commit (93c3b3d4) that silently ignored CWD-relative ./.tui config and crashed before Main on malformed config. Verified under .2 that a ./.tui/config.json with {"Theme":"Light"} in the launch CWD now takes effect (tuirec casts show Light-theme colors vs. an identical-config-free baseline).

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https://claude.ai/code/session_01BVbLXNzbus2MTXmiJDBErL