test(e2e): port sync tests to B2 cursor contract (pairs with plugin #109)

[Rasbandit]

Summary

Adapts the Obsidian E2E suite to the B2 cursor-pull sync contract (plugin PR engram-app/Engram-obsidian#109). B2 replaced the legacy timestamp feed with an ordered cursor pull, which changes two behaviors these tests asserted:

1. lastSync is frozen — the opaque syncCursor is the watermark now, so "lastSync advances after a sync" is obsolete.
2. Bootstrap pushes offline-created files inside bootstrap() — a fullSync push counter can read 0 even though the file reaches the server.

Changes:

• e2e/helpers/cdp.py — add get_sync_cursor() (reads syncEngine.getSyncCursor()).
• test_58_commands_palette / test_59_status_bar_click — assert the command/click actually pulls a pending server change (create a server note → run sync-now / click → assert it arrives locally), instead of asserting lastSync changed.
• test_44_oauth_device_flow — assert the created note arrives on the server (the in-file GET /notes/{path}), instead of asserting the fullSync push count ≥ 1.

Verification

The paired e2e (this branch + plugin feat/sync-cursor-pull-b2) is green — run 27667988219: 109 passed. That run also validated the plugin-side B2 fixes (reconnect catch-up after a vault swap; offline-queue recovery).

Merge note

This pairs with plugin #109 (chicken-and-egg): these ported tests assert B2 behavior, so they fail against plugin main (pre-B2). Merge order: plugin #109 first (B2 → plugin main), then this PR — at which point its auto-triggered e2e runs against a B2 plugin main and passes. Detail in workspace docs/context/b2-cursor-pull-e2e-triage.md.

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