docs(changelog): unreleased — settings template defaults to Opus 5

Records the pi-toolkit 926f738 template change (defaultModel + pi-fork deep
tier -> eu.anthropic.claude-opus-5). No tag, no build: CI resolves the
pi-toolkit SHA from main at build time, so whichever release builds next
picks it up.

CHANGELOG.md

@@ -13,7 +13,23 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
 
 ## Unreleased
 
-_Nothing yet — next release's changes will accrue here._
+### Changed
+
+- **Settings template now defaults to Claude Opus 5** (`pi-toolkit` @ `926f738`).
+  `settings.example.json` — the file `entrypoint-user.sh` bootstraps
+  `~/.pi/agent/settings.json` from — moves `defaultModel` and the `pi-fork`
+  **deep** tier from `eu.anthropic.claude-opus-4-8` to
+  `eu.anthropic.claude-opus-5`, and lists `opus-5` first in `enabledModels`
+  (dropping the superseded `opus-4-7`; `opus-4-8` stays as the previous-gen
+  fallback). `fast` = `haiku-4-5` and `balanced` = `sonnet-5` are unchanged.
+  Opus 5 shipped to users in v1.6.3 via pi `0.82.1`, but nothing in the image
+  actually pointed at it. **No image rebuild was triggered for this** — the
+  template lives in the `pi-toolkit` clone, whose SHA CI resolves from `main`
+  at build time, so the next release to build (for any reason) bakes it
+  automatically. Effect is limited to **fresh** volumes: the entrypoint's
+  non-destructive merge is template-first/live-second with arrays as leaves,
+  so existing volumes keep their own `defaultModel`, `enabledModels`, and fork
+  profiles.
 
 ## v1.6.3 — 2026-07-25