Complete docfx deep-dive review planning for all documents

[Copilot]

Proposed Changes/Todos

• Scope completion
  • Covered every markdown deep-dive doc under /docfx/docs (36 total); no partial batches left.
• Per-document plan artifacts
  • Added one plan file per doc in /plans, with strict 1:1 mapping (36 docs -> 36 plans).
  • Each plan captures: source-backed accuracy checks, completeness targets, consistency/grammar normalization, xref validation, Mermaid GitHub-compat checks, separator/em-dash cleanup, and C#14 example conformance.
• Cross-doc enforcement encoded in each plan
  • No horizontal separators between headings.
  • No em-dashes; use semicolons/parentheses.
  • Prefer <xref:...> API links and resolve/normalize existing references.
• High-signal file-specific corrections queued
  • Popovers.md: Application.Popover -> Application.Popovers.
  • layout.md: AnchorEnd (10) -> Pos.AnchorEnd (10).
  • config.md: Mermaid graph TD -> flowchart TD.
  • lexicon.md: normalize include path style to ~/includes/....
• Deep-dive inventory recommendations captured
  • Candidates to add: input pipeline end-to-end troubleshooting, driver troubleshooting matrix, scheme/theme inheritance debugging.
  • Candidate to merge: command-diagrams.md into command.md (if duplication reduction is preferred).

# Plan for Popovers.md

## Planned Actions
- [ ] Verify technical claims against source code in ApplicationPopover/IApplication.
- [ ] Replace all `Application.Popover` references with `Application.Popovers`.
- [ ] Validate and correct all xrefs; use `<xref:...>` where possible.
- [ ] Remove em-dashes; keep no horizontal separators.
- [ ] Ensure Mermaid (if added) is GitHub-compatible.

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[tig]

Not really needed. closing