Fixes #3849. Docs: clarify when to use -ing vs -ed events (Accepting vs Accepted, etc.)

[Copilot]

AI agents and IntelliSense autocomplete consistently reach for -ing events (Accepting, Activating) for simple side-effect handlers that should use -ed events instead. The -ing variants run synchronously mid-dispatch and are cancellable — subscribing without cancelling is both wasteful and misleading.

Changes

• docfx/docs/events.md — New "When to Use -ing vs -ed Events" section added near the top with the canonical rule, concrete ✅/❌ examples, and a quick-reference table covering all common pairs.

• .claude/rules/event-patterns.md — Same rule added as the first section so Copilot/Claude sees it immediately when reading event guidance.

• View.Command.cs XML docs — <remarks> added to all four paired command events:

  • Accepting / Accepted
  • Activating / Activated

Rule (now in docs, xmldoc, and AI rules)

// ✅ side-effect — use the -ed event
button.Accepted += (_, _) => DoTheThing ();

// ✅ needs to cancel — -ing is correct
button.Accepting += (_, e) => { if (!CanProceed ()) e.Handled = true; };

// ❌ handler ignores EventArgs — should be Accepted
button.Accepting += (_, _) => DoTheThing ();

If your handler doesn't read or set anything on EventArgs (no e.Handled, no e.Cancel), use the -ed event.

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