document test layers and Claude's UI workflow

Three docs under docs/testing/:

  * README.md — layer-by-layer reference (what each covers, the
    runner, how to invoke, local vs CI flow). Points at the load-
    bearing startup gate and the client-side-only constraint so a
    macOS clone runs the same suite as Linux.
  * a11y-manual.md — 15-minute manual checklist run at every tier
    cut. Orca on Linux, VoiceOver on macOS. Catches prose drift
    automation can't judge.
  * claude-ui-workflow.md — how Claude Code drives the WASM build
    through Playwright, including the `flt-semantics-placeholder`
    quirk (semantics are opt-in in Flutter web; the driver
    auto-clicks the placeholder to enable them).

Co-Authored-By: Claude <noreply@anthropic.com>

docs/testing/a11y-manual.md

@@ -0,0 +1,47 @@
+# Manual a11y checklist — run at every tier cut
+
+Automated a11y tests catch structural regressions (missing Semantics,
+broken contrast, missing i18n keys). They don't catch "this label is
+technically correct but reads like robot noise." A 15-minute manual
+pass at every tier cut does.
+
+## Linux — Orca
+
+1. Start Orca: `orca -s` (settings), toggle on "Focus follows mouse".
+2. Launch clide: `flutter run -d linux` or the built bundle.
+3. Tab through every slot in order. Every stop should read
+   - panel name, then
+   - a one-line verb describing what the widget does.
+4. Open the command palette (`ctrl+k` once it's wired). Read each
+   command out loud. Flag commands whose name alone doesn't make
+   it obvious what they do.
+5. Open the theme picker. Orca should announce "Select theme", then
+   read each row as "theme name, activate this theme". Selecting
+   announces the new theme.
+6. Disconnect the daemon mid-session. Orca should announce the
+   statusbar change (it's a live region).
+
+## macOS — VoiceOver
+
+VoiceOver: `cmd+F5`. Same checklist as Orca. Extra pass:
+- Rotor navigation (`ctrl+opt+u`) should list every Semantic
+  landmark; no "unknown group" entries.
+- Per-element hints read cleanly when pressing `ctrl+opt+shift+h`.
+
+## Report a drift
+
+Any label that feels off — noise, tech jargon, abbreviations screen
+readers mispronounce — becomes a follow-up ticket. Do not "fix" in
+the branch being cut; queue it so each tier stays focused. File
+under `docs/todo-a11y.md` (create if absent) with:
+
+```
+- [ ] ext.<id>: <key-or-widget> — <what's wrong>, <suggested wording>
+```
+
+## Why this isn't automated
+
+Automation catches structural violations. Automation can't judge prose.
+A 15-minute human pass per tier stays cheap and catches the gap.
+Revisit automation (axe-core via Playwright, Flutter a11y harnesses)
+if we ship a public build.