docs(testing): web e2e lane docs + Agent Note to implemented

testing.md gains the web browser snapshot tier entry (divergent
DSH_SNAPSHOT=... test:web commands) and names apps/web/tests/snapshots/
as the web surface's snapshot home. The GUI testing note's tier map and
lane map gain the e2e scenarios (both languages, pair re-recorded) and
drop the stale verify-session-real references (those scripts left with
the missions/ tree). packages/client/AGENTS.md check ladder covers the
wire-carriage trigger and refresh/record commands. acp-snapshot README
stops claiming the whole package is ACP-specific — its normalizers are
transport-neutral with three consumers now. vitest.web.config.ts header
carries TODO(ci-browser) with the staged-reversal pointer.

The design-study Agent Note moves proposed/ -> implemented/ rewritten in
present tense: all review decisions recorded (llm:false seam over the
placeholder-key hack, providers-mode replay, whenIdle barrier stack,
single aria golden + anchors, TUI-style inline modes over a suite
factory, scrub-only header stance, CI deferral) with re-entry triggers
under Deferred.

apps/web/tests/harness.ts

@@ -243,11 +243,11 @@ export function rawSessionLog(session: Session): string {
 
 /**
  * Record-mode fixture write-back: harvest the live session, scrub request
- * headers to {{system}}/{{tools}} (the web lane pins no header class — a
- * deliberate deviation logged in the Agent Note's deferred work), tokenize
- * the run-local session id and cwd ({{sessionId}}/{{cwd}}, the committed ACP
- * fixture convention — re-records then diff only on real content), and write
- * the committed fixture.
+ * headers to {{system}}/{{tools}} (TODO(web-header-pin): the web lane pins no
+ * header class — a deliberate deviation logged in the Agent Note's deferred
+ * work), tokenize the run-local session id and cwd ({{sessionId}}/{{cwd}},
+ * the committed ACP fixture convention — re-records then diff only on real
+ * content), and write the committed fixture.
  * @param harness - the record-mode harness.
  * @param sessionId - the driven session.
  * @param fixturePath - the committed session.jsonl / seed.jsonl target.