RFC: SharpConsoleUI command center for the interactive shell

[nickprotop]

What this is

A working prototype that replaces the prompt-first interactive shell (bare dotnet skills / agents) with a retained-mode SharpConsoleUI command center — the direction your docs/cli-rewrite-plan.md flagged as a possible later phase.

Opening as a draft for feedback on direction, not as a merge-ready change.

Demo

![SharpConsoleUI command center — Bundles page with bundle-detail modal]

How it works

• InteractiveConsoleApp → partial. The original Spectre.Console.SelectionPrompt loop is preserved as RunClassicShellAsync and used automatically when stdin/stdout is redirected (CI, pipes, dumb terminals). The new RunAsync is the SharpConsoleUI shell.
• InteractiveConsoleApp.Shell.cs adds the ConsoleWindowSystem + NavigationView with pages for every HomeAction surface (Home, Skills, Installed, Collections, Bundles, Packages, Agents, Project, Analysis, Remove-all, Update-all, Settings, About) — driven by the existing NavigationSurfaceManifest.
• Page content reuses the existing BuildRich* Spectre renderables verbatim, hosted in SpectreRenderableControl — no rendering rewrite in this PR.
• Selection flows: ListControl activation → modal Windows with a ToolbarControl row of ButtonControls. Mutations call the Runtime/* installers (SkillInstaller, AgentInstaller, ProjectSkillRecommender) directly and re-render the page in place.
• Interactive bottom status bar (StatusBarControl, lazynuget / cxfiles style): dynamic per-page hints, clickable items, shortcut highlighting, ticking clock, live catalog summary, toast slot for action results. Ctrl+R / Ctrl+U / Ctrl+I shortcuts are also wired through the window's key handler so they actually fire.
• Main window: rounded subtle border, hidden title, Maximized(); Esc and OnClosed both call ws.Shutdown(0). Modals: centered, non-minimizable / non-maximizable, Esc dismisses.
• List selection theme is pinned so keyboard / mouse hover / mouse click all paint the same solid selection bar (otherwise HighlightBackgroundColor, ListHoverBackgroundColor, and ListUnfocusedHighlightBackgroundColor paint three different colours).
• SharpConsoleUI 2.4.55 → 2.4.61, and added to ManagedCode.DotnetSkills.csproj — the main tool had no SharpConsoleUI reference yet; the dep was only declared in the agents / dotnet-agents wrappers, which compile the same sources.

Status

• All four projects build clean (ManagedCode.DotnetSkills, ManagedCode.Agents, ManagedCode.DotnetAgents, ManagedCode.DotnetSkills.Tests).
• All 613 tests pass.
• dotnet skills <subcommand> (list / install / recommend / bundle list / agent install / …) is unchanged — only the bare interactive invocation is affected.
• Action flows are intentionally simpler than the classic shell in places (single-select + confirm vs. multi-select with layout pickers). Catalog refresh and per-page mutations re-render in place via the new live state plumbing.

What's next if you like the direction

This PR keeps the Spectre Panel / Grid / Table renderables behind SpectreRenderableControl so the visual identity is preserved with minimum churn. Phase 2 — only worth doing if you want to commit to this surface — is replacing those with native SharpConsoleUI controls (PanelControl, TableControl, HorizontalGridControl, MarkupControl, …). That buys: per-row mouse interactivity, proper layout reflow, theme integration, no Spectre-renderable-in-a-buffer-cell quirks. Same page contracts, swap the leaf builders.

Questions for the maintainers

1. Is this a direction you want dotnet-skills to take, given the cli-rewrite-plan.md framing?
2. Full-screen alt-buffer TUI as the default for bare invocation vs. an opt-in (--ui / --shell)? Today CI and pipes already fall through to the classic shell automatically; the question is what a real-terminal user sees by default.
3. If yes to direction — would you want Phase 2 (native controls) as a follow-up PR, or is the Spectre-renderable-in-a-control approach in this PR sufficient?