docs: correct stale architecture references

Found by a docs/ staleness audit:
- architecture.md: Claude no longer runs under tmux — it's driven over
  the stream-json control protocol with --resume (D-75/D-77/D-78); and
  the IPC socket server is implemented, not "currently unimplemented".
- testing/README.md + claude-ui-workflow.md: drop the dissolved app/
  two-package paths (D-56) — tests live at test/ and the web build at
  build/web/.
- design/multitab-pane.md: the Claude pane spawns a stream-json session,
  not a tmux one; ClaudeSessionRef carries the session id.

Frozen historical snapshots (initial-plan.md, the HISTORICAL pty docs,
dated spikes/audits) left as-is.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/testing/README.md

@@ -8,10 +8,10 @@ on any Linux or macOS dev box without network access or shared state.
 
 | layer | location | runner | time | when |
 |---|---|---|---|---|
-| unit (root) | `test/` | `dart test` | ~5s | `make test` |
-| unit + widget + golden (app) | `app/test/` | `flutter test` | ~30s | `make test` |
-| a11y contract | `app/test/a11y/` | `flutter test` | ~5s | `make test-a11y` |
-| integration (startup gate) | `app/integration_test/` | `flutter test integration_test/` | ~60s | `make test-integration` |
+| unit (Flutter-free core) | `test/ipc/`, `test/daemon/`, `test/pty/` | `dart test` | ~5s | `make test-core` |
+| unit + widget + golden | `test/` | `flutter test` | ~30s | `make test` |
+| a11y contract | `test/a11y/` | `flutter test` | ~5s | `make test-a11y` |
+| integration (startup gate) | `integration_test/` | `flutter test integration_test/` | ~60s | `make test-integration` |
 | daemon E2E + web WASM smoke | `test/daemon/` + `tools/ui/tests/` | `dart test` + Playwright | ~60s | `make test-e2e` |
 | startup bundle smoke | `ci/smoke_bundle.sh` | xvfb-run, 5s timeout | ~30s | `make smoke-bundle` |
 

docs/testing/claude-ui-workflow.md

@@ -4,7 +4,7 @@ Claude Code needs to *actually use* the app while building features.
 The pipeline:
 
 1. **Flutter builds the app to WASM.** `flutter build web --wasm` ships
-   a CanvasKit/Skwasm bundle under `app/build/web/`.
+   a CanvasKit/Skwasm bundle under `build/web/`.
 2. **A local server serves it.** `tools/ui/serve.sh` starts
    `http://localhost:4280` in the background with a pidfile.
 3. **Playwright drives a headless Chromium.** Instead of click-by-pixel