feat(gre): back-to-Home nav — bump anki pin + docs (engine lane)

[f15cubing]

What & why

Bumps the anki submodule pin e4efa0f6 → 1f42b3d to bring in the GRE cross-surface "← Home" navigation (fork PR f15cubing/anki#5): a shared GreHomeLink.svelte + new gre:home webview bridge on the dashboard/method/exam surfaces so users can return to GRE Home, plus bigger Home "Your progress" numbers. Pure presentation UI.

Area(s) touched

anki (gitlink pin), docs/codebase/qt.md, docs/codebase/INDEX.md, docs/STATUS.md — engine/Rust PR? yes (submodule pin) — but UI-only, no engine code.

Docs updated

docs/codebase/qt.md (§ cross-surface navigation + Last-verified SHA → 1f42b3d), new INDEX.md row, STATUS.md entry.

Test evidence

Fork side: ./ninja check:svelte Build succeeded; svelte-check 0 errors/0 warnings; changed .py compile. No collection writes.

Engine/Rust extra gate

• Undo / no collection corruption: N/A — no col writes, no OpChanges, read paths unchanged.
• Read-only invariant / new RPC: N/A — no new RPC, no Rust.
• DO NOT SELF-MERGE. Two gates remain and are owner-gated:
  1. Live GUI click-through of the ← Home button on dashboard/method/exam (offscreen QtWebEngine won't init headlessly).
  2. Second-agent review — the agent reviewer is currently billing-blocked; the repo precedent (feat(gre): re-bundle interactive-MCQ deck into both apps + bump GRE_DECK_VERSION (2026-07-03b) #40) is builder self-review + documented deviation if you choose to waive.

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