Document dashboard terminals and AppHost terminal interactions for 13.6

@mitchdenny is already working on this.

Since Sep 15, 2026.

## Summary

Audit and update all terminal-related Aspire documentation for the features in microsoft/aspire#19887. This is the consolidated documentation follow-up for 13.6, covering both resource terminals and AppHost-owned terminals rather than only the dock's empty-state help link.

## Documentation scope

- Explain resource terminals configured with `WithTerminal(...)`, supported processes, prerequisites, and the dashboard Terminal view.
- Document AppHost-owned terminals, `TerminalService`, `AspireTerminal`, and the flattened `TerminalLaunchOptions` configuration (executable, arguments, working directory, environment variables, dimensions, title, and placement). Keep the public examples Hex1b-free.
- Cover the terminal dock: opening it from the header or keyboard shortcut, AppHost-triggered activation, tabs, hiding versus closing, resizing, and font controls. Explain why it is unavailable in a standalone OTEL-only dashboard.
- Cover detached windows for resource and dock terminals, returning to the dock, window reuse, browser popup restrictions, and the distinction between closing a viewer and stopping its producer.
- Document the dedicated `PromptTerminalAsync` interaction and its options/context, following the progress-dialog Work/completion/cancellation model. Migrate examples away from `InputType.Terminal` and terminal-valued form inputs.
- Make ownership explicit: the caller creates, starts, and disposes the terminal; an interaction borrows it and does not stop or dispose it. Completion/cancellation and process exit are separate, and the same terminal can be reused across prompts.
- Audit supported terminal automation and CLI workflows against the final implementation, including sending input/keys and waiting for output; document limitations without inventing unsupported commands.
- Include practical examples such as an authentication flow, a shell, container exec, and the automated number-guess playground. Review accessibility, focus navigation, platform differences, and terminal/security limitations.
- Remove stale terminology and configuration examples, including the former Hosting `TerminalCommand` launch configuration type. Preserve references to the unrelated CLI command implementation where appropriate.

## Help link and acceptance criteria

- [ ] Publish a discoverable dashboard terminals guide and update existing terminal pages, API references, examples, and navigation links.
- [ ] Provision **https://aka.ms/aspire/dashboard-terminals** to the published guide. The dashboard's empty dock links here; creating this issue does **not** provision the redirect.
- [ ] Verify the alias resolves to the intended published page before shipping.
- [ ] Validate examples against the final 13.6 API and cross-link relevant resource, interaction, and CLI documentation.
- [ ] Coordinate existing terminal documentation work, including microsoft/aspire.dev#1282 and microsoft/aspire.dev#1246, without duplicating their implementation-specific tasks.

Implementation reference: https://github.com/microsoft/aspire/pull/19887
Design/behavior reference: `docs/specs/with-terminal.md` in microsoft/aspire.