[docs] decision: navigation is awaited with expect_navigation / wait_for_url / wait_for_load_state

[AutomatedTester]

💥 What does this PR do?

Proposes a design decision record: navigation is awaited with expect_navigation / wait_for_url / wait_for_load_state.

A click that triggers navigation is a top source of flaky tests: act-then-wait races because the navigation can complete between the two steps. BiDi emits the full navigation lifecycle (navigationStarted/navigationCommitted/domContentLoaded/load/navigationFailed/…), and with the expect_* primitive (record 0001, #17671) these become race-free waits. This record proposes the established Playwright-shaped trio: expect_navigation() (arm-before-action), wait_for_url(), and wait_for_load_state() with a shared commit/domcontentloaded/load vocabulary, consistent across bindings.

🔧 Implementation Notes

• Follows the docs/decisions/ process from [docs] add design decision record process and template #17665 — depends on [docs] add design decision record process and template #17665 landing (adds only docs/decisions/0006-*.md).
• Builds on the expect_*/Subscription primitive proposed in [docs] decision: BiDi events are awaited with expect_* context managers #17671 (record 0001), which should land first.
• Failed/aborted navigations surface as an error within the wait, not a silent timeout. No wire-protocol change.

🤖 AI assistance

• AI assisted (complete below)
  • Tool(s): Claude Code
  • What was generated: Initial draft of the decision record, derived from a CDDL-validated comparison of the Python BiDi surface against Playwright; revised through discussion and review
  • I reviewed all AI output and can explain the change

💡 Additional Considerations

One of a set of BiDi ergonomics decision records proposed together. Cross-binding convergence is tracked in the binding-status table.

🔄 Types of changes

• Documentation (design decision record)