docs(window-switcher): write down what the build cost to learn

The component is finished and on the user's ALT+TAB, so what is left is the
part that would otherwise have to be rediscovered. Most of the time this
build took went to three things that report success and then do nothing:
Hyprland 0.56.2 evaluating dispatch arguments as Lua, so the
documented-looking `focuswindow address:0x...` is a silent syntax error; a
focus dispatched while the overlay still holds an exclusive keyboard grab
being accepted and ignored; and a sort on a `focusHistoryID` property that
does not exist, comparing NaN and leaving an arbitrary order that looks
plausible. None of them logs anything.

Those six, plus the missing `0x` prefix, the empty `toplevels` before
`refreshToplevels()` and `ScreencopyView` reporting (-1, -1) rather than
(0, 0), generalise past this component, so they go in AGENTS.md next to the
other notes that exist because a commit message explained itself once. The
card geometry and the blank icon square are specific to the grid and stay in
the component README.

Also corrects the counts that four components made true and five do not: the
component lists, "the other three use ExclusionMode.Ignore", and the Theme
symlink note.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SYg4wYHq5XNbiVmMeKRb1S

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