docs(e2e): reconcile the docs with what this branch actually contains

The two doc commits were written against a lineage where the
selectClaudeModel spec fix lived on a separate branch, which left three
stale claims after the rebase:

- e2e/llm.ts still called selectDemoModel a known gap and pointed at a
  docs section title that no longer exists; the specs in this very
  branch already use selectClaudeModel. Replace the paragraph with the
  current behavior.
- docs/e2e-ci.md attributed the fix to "the e2e suite branch (#220)";
  this branch carries that commit itself, so say so and name the commit.
- The 23/4 keyless and 27/0 with-key figures were presented as bare
  facts ("verified locally"). Attribute them to where they were actually
  measured - the spec-fix commit's own verification against a full local
  stack - and state they have not been re-measured since the rebase onto
  current main. Drop the unattributed "~7 minutes" typical-run figure in
  favor of the structural 27-spec / 4-gated breakdown (confirmed by
  `npx playwright test --list`: 27 tests in 7 files).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>