docs: index the screenshots, and drop the ones that showed nothing

Co-Authored-By: Claude Opus 5 <[email protected]>

docs/screenshots/README.md

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+# Screenshots from the classroom v2 experiment
+
+All 1920×1080, captured with `grim` from a real running session in the
+container lab. See [../classroom-v2-experiment.md](../classroom-v2-experiment.md).
+
+## The desktop
+
+| | |
+| --- | --- |
+| `v2-idle-desktop` | the idle desktop: the wallpaper, one bar, nothing else |
+| `v2-from-package` | the same desktop, produced by installing the `.deb` on a clean machine |
+| `v2-dark-bar`, `v2-light-bar` | the bar in both themes |
+| `v2-theme-compare` | the two, one above the other |
+| `v2-testpage` | a maximised browser, edge to edge above the bar |
+| `v2-wonderink` | Wonder Ink as an application, in its own profile |
+
+## Application state
+
+| | |
+| --- | --- |
+| `state-1-closed` | both launchers closed: no indicator |
+| `state-3-behind` | one active (teal), one running behind it (grey) |
+| `state-4-minimized` | minimised — measured identical to *behind*, which is why minimise was removed as a route |
+| `state-5-restored` | back |
+| `v2-both-apps` | both applications, one button each, from the packaged install |
+| `labelled-tasks` | the labelled task manager, evaluated and rejected: it shows changing page titles rather than application names |
+
+## Windows
+
+| | |
+| --- | --- |
+| `v2-secondary-window` | a window a page opened, floating over an untouched browser, with its own close button |
+| `v2-print-dialog` | the system print dialog, over the page that raised it, offering only Elmer |
+| `v2-fullscreen` | fullscreen video: the whole display, panel covered |
+| `v2-layershell` | a gtk-layer-shell overlay under KWin — what the DVD loading cover is made of |
+| `v2-notification-crop` | a notification card, top right |
+
+## Reliability and lockdown
+
+| | |
+| --- | --- |
+| `recovery-after-8-kills` | the panel after eight consecutive SIGKILLs |
+| `recovery-after-kwin-kill` | the session after KWin was killed twice; the application window survived |
+| `recover-panel` | the bar rebuilt from the layout script after its configuration was deleted |
+| `lock-desktop-rmb` | right-clicking the wallpaper: no menu |
+| `lock-panel-rmb` | right-clicking the bar: no menu |
+| `lock-krunner` | KRunner asked for, and not there |
+
+## Failures, kept
+
+| | |
+| --- | --- |
+| `wtype-probe` | keyboard injection never reached the nested session, so every interaction in this experiment was driven by the pointer instead |
+| `m-closed`, `m-minimized` | the pair whose pixels were sampled to show that Plasma draws minimised and closed differently, but minimised and *behind* the same |