feat(theme): make Boreal the distro default

Seed theme-state.json and the downstream template from themes/boreal.json
(including border + empty settings). Point eval/schema fallbacks at Boreal
(theme.nix preset, plymouth and live-ISO splash colors, theme-shot, sync
error examples). Docs/TESTING and RECOVERY follow the new default.

Verified: state matches boreal palette; theme-contrast all pass.
preview.png for boreal still missing (picker plain-name; V3 capture).

agent/BACKLOG.md

@@ -28,15 +28,6 @@ in [`docs/ROADMAP.md`](../docs/ROADMAP.md); map in
 
 ## NEXT
 
-### 42. Default theme → boreal (`VISION § B` / v1.0 bar)
-Ship Boreal as the distro default instead of Tokyo Night: root
-`theme-state.json`, `templates/downstream/theme-state.json` (and any
-greeter/plymouth fallbacks that hardcode Tokyo Night when state is
-missing). Preset already exists under `themes/boreal/`. Capture
-`preview.png` if still missing so the picker looks first-class.
-Cost: copy/apply palette into seed state files + grep for tokyo-night
-defaults; V0 contrast, V1/V2 theme apply, V3 visual on hardware.
-
 ### 43. System › Firmware — fwupd product surface (`VISION § A`)
 `services.fwupd.enable` is already default-on and never auto-flashes,
 but users only learn about `fwupdmgr` from a README sentence. Add a
@@ -131,10 +122,12 @@ implement. Bernardo moves accepted items into a tier.*
 
 ### v1.0 track — see `docs/VISION.md`
 
-Product themes and the release bar live in **VISION**. Promoted to
-**NEXT:** #42 boreal default · #43 System › Firmware · #44 doctor
-hardware. Remaining candidate promotions: fingerprint menu ·
-first-boot tips · human rebuild errors · neon-glass quarantine.
+Product themes and the release bar live in **VISION**. **NEXT:**
+#43 System › Firmware · #44 doctor hardware. #42 boreal default
+shipped (seed state + eval fallbacks); still missing
+`themes/boreal/preview.png` (picker plain-name until captured).
+Remaining candidate promotions: fingerprint menu · first-boot tips ·
+human rebuild errors · neon-glass quarantine.
 
 ### Pre-existing
 
@@ -283,11 +276,12 @@ first-boot tips · human rebuild errors · neon-glass quarantine.
 ### Theme polish / completeness (codebase exam 2026-07-09)
 
 - **Missing theme picker previews + hand btop for identity themes**
-  `boreal`, `executive-slate`, and `neon-glass` lack `preview.png`
-  (picker falls back to plain-name rows) and `btop.theme` (generated
-  btop only). CSS/jsonc for boreal/executive-slate are otherwise
-  solid. Capture previews after neon-glass is fixed/quarantined.
-  Cost: asset capture + optional hand btop; V3 visual.
+  `boreal` (now the default — higher priority), `executive-slate`, and
+  `neon-glass` lack `preview.png` (picker plain-name rows) and
+  `btop.theme` (generated btop only). CSS/jsonc for boreal/executive-slate
+  are solid. Capture boreal preview ASAP for v1.0 bar; others after
+  neon-glass is fixed/quarantined. Cost: asset capture + optional hand
+  btop; V3 visual.
 
 - **Generated Waybar missing identity-bar affordances**
   Whole-swap bars ship `custom/powermenu` and a left logo → main menu;