fix: disk picker fd0 (#112), menu Back guard (#106), offline theme (#113)

- #112: list_installable_disks drops fd/loop/sr/zram/<8GiB, largest-first
  so OVMF no longer offers /dev/fd0 as the default wipe target
- #106: tools/check-menu-back.py + checks.menu-back (proved to fail)
- #113: offline theme-switch contract documented (default/pinned only);
  theme-sync run_switch adds offline-oriented hint when no network

Verified: V0 flake check; installer-safety; menu-back; py_compile.

agent/JOURNAL.md

@@ -19,6 +19,19 @@ Template:
 
 ---
 
+## 2026-07-15 — Fix batch #112 disk picker, #106 menu Back, #113 offline theme
+- **Task:** Second fix-only batch from NEXT/NOW residuals.
+- **Did:** (112) `list_installable_disks` excludes fd/loop/sr/zram/tiny
+  (<8 GiB), sorts largest-first; installer-safety markers. (106)
+  `tools/check-menu-back.py` + `checks.menu-back` (proved to fail when Back
+  stripped). (113) offline theme contract: TESTING item 6 scoped to default/
+  current theme; `run_switch` prints clear offline-oriented message on
+  network/build failures.
+- **Verified:** V0 flake check; installer-safety; menu-back prove-fail;
+  py_compile theme-sync.
+- **Pending:** V2 unattended install with OVMF fd0 present (optional).
+- **Next suggestion:** #108 keybinds audit, or #94 test-install chromium.
+
 ## 2026-07-15 — Fix batch #123–#126 (install bake, flake ref, ISO name, display)
 - **Task:** Fix-only NOW batch: #123 dconf pre-activate, #124 main flake
   seed, #125 ISO filename, #126 display mode list.