docs(backlog): settle #107 on state.json

Bernardo's call — the rename target is decided, so drop the alternative
rather than leave whoever picks the item re-opening it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -100,9 +100,9 @@ pre-existing ISO-pinning gap.
 The state file long ago stopped being about themes: it carries night-light,
 keyboard memory, display resolution and profiles, auto-commit, services and
 more, so `theme.json` now misnames its own contents and misleads anyone
-reading the flake. Rename it to `state.json` (Bernardo, 2026-07-14 —
-`system.json` is the alternative; pick one and use it everywhere), and carry
-the `nomarchy-theme-sync` tool name along with it.
+reading the flake. Rename it to `state.json` (Bernardo's call, 2026-07-14 —
+settled, do not revisit), and carry the `nomarchy-theme-sync` tool name along
+with it.
 
 Standalone task — do not fold it into a feature. Ships with a compatibility
 shim that keeps reading an existing `theme.json` so downstream checkouts do