Add Simple-mode support to e2e tests

Summary

The e2e suite currently only runs against Power interface mode. As of paranext-core
a77a65528a
("PT-3958: 10Simple layout styling adjustments", #2585),
Simple mode — the default (platform.interfaceMode defaults to 'simple') — hides the Home and
Editor columns' tab bars entirely (headless, pointer-events: none) and ships a Resources column
whose default tabs (Model Text, Commentaries, ...) never resolve real titles on a bare e2e profile
with no configured resources.

That broke both the strict cold-start readiness gate and the WEB-tab click flow (see PR #169 for
the CI failure screenshots). PR #169 works around it by seeding platform.interfaceMode: 'power'
into every e2e launch (E2E_SETTINGS_OVERRIDES in e2e-tests/fixtures/helpers.ts), which restores
the old visible/clickable dock-tab behavior the suite was written against. That's a stand-in, not
real coverage: the suite currently asserts nothing about how the Interlinearizer actually behaves
under Simple mode, which is the default UI real users see.

What needs to change

• Readiness gate. waitForDockTabTitlesResolved (e2e-tests/fixtures/helpers.ts) requires
  every .dock-tab to resolve a real title in strict/cold-start mode. In Simple mode this can never
  be satisfied by a fresh profile, since the Resources column ships default tabs (Model Text,
  Commentaries) with no backing resource configured. Simple-mode readiness needs its own definition —
  e.g. only gate on the tabs the Interlinearizer flow actually touches, not every default Resources tab.
• Navigation flow. openInterlinearizerFromScriptureEditor and ensureInterlinearizerOpenOnWeb
  assume a visible, clickable .dock-tab for the Scripture Editor / WEB project. In Simple mode the
  Editor column's tab bar is headless and collapsed, so the existing tab-click flow can't be reused
  as-is — needs a Simple-mode-aware way to confirm/focus the loaded project (the fixed column itself
  may already be focused, or a different affordance needs to be used).
• Home flow. The Home-button-based project-opening flow may also need adjusting: Simple mode's
  Home column is a fixed, headless-tab-bar column (always present), not the closable floating tab the
  current helper comments describe for a "fresh core profile."
• Test matrix. Decide whether both tiers (smoke + CDP) run twice (once per interface mode) or
  whether Simple-mode coverage is added more narrowly (e.g. one dedicated smoke test), given the
  runtime cost of a second full Electron cold start per tier.

Constraints

• Don't regress existing Power-mode coverage — it should keep exercising the same flows it does today.
• platform.interfaceMode is validated to only 'simple' | 'power'
  (core-settings-info.data.ts), so seeding is a simple key, not new infrastructure.
• Reuse the existing settings-seed/backup mechanism (E2E_SETTINGS_OVERRIDES,
  backupAndSeedSettings/restoreBackedUpSettings in e2e-tests/fixtures/helpers.ts) rather than
  building a parallel one.

Start in e2e-tests/fixtures/helpers.ts with waitForDockTabTitlesResolved, openInterlinearizerFromScriptureEditor, ensureInterlinearizerOpenOnWeb, and the E2E_SETTINGS_OVERRIDES flow. Compare the existing Power-mode behavior with Simple mode and review PR #169's CI failure screenshots. Done means Simple-mode coverage works without regressing Power-mode coverage, using the existing settings backup and restore helpers.