docs: capture local Grav core upgrade + refresh version-authority docs

New learning: docs/solutions/tooling-decisions/upgrade-local-grav-core-rebuild-docker-image.md
— the local Grav core is baked into the Docker image (only ./user is bind-mounted),
so it upgrades by a Dockerfile URL bump + image rebuild + `docker rm -f` recreate,
not the `gpm self-upgrade` the servers use (non-durable in-container).

Refreshed three docs this exposed as stale/incomplete:
- local-setup.md: rewrote the stale "newer Grav RC" section with the durable
  rebuild procedure (recreate gotcha, verify, plugin refresh, non-durability note).
- deploy-cycle.md: Phase 0 now upgrades the local core; state-model notes the
  image as a fourth surface beyond the three server layers.
- stale-grav-version-blocks-api-plugin-install.md: version-authority surfaces
  3 -> 4 (hardcoded Dockerfile URL); clarified .env* GRAV_VERSION governs fresh
  remote installs only, never the local Docker core.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Np4cMQLF77i664CAQXySzU

docs/guides/deploy-cycle.md

@@ -34,6 +34,11 @@ Referenced gotcha docs:
 - `docs/solutions/architecture-patterns/git-sync-secret-exposure-and-tracked-file-boomerang.md` — gitignore is the sync boundary; env-tree leak.
 - `docs/solutions/conventions/grav-plugin-config-must-be-tracked-override.md` — plugin config must live in the tracked override.
 
+These three layers describe the **servers**. Locally there is a fourth: the Grav
+**core** is baked into the Docker **image** (`Dockerfile`), not in any layer above —
+so the local core upgrades by an image rebuild, never by the `gpm self-upgrade` the
+servers use. See `docs/solutions/tooling-decisions/upgrade-local-grav-core-rebuild-docker-image.md`.
+
 ---
 
 ## Phase 0 — Local (author + prove the change)
@@ -42,7 +47,8 @@ Referenced gotcha docs:
    - GPM channel: `gpm.releases: stable` in `user/config/system.yaml` (authoritative; reaches servers via content pull, so it must be right **before** any server GPM op).
    - `plugins.txt` — the GPM-managed set only. **Never** add `git-sync` (it is remote-only).
    - Prod-only overrides (Twig cache/debug, `debugger.shutdown.close_connection: false`) in `deploy/env/prod/system.yaml` — **never** commit prod values into `user/config/system.yaml`.
-   - **Bump `GRAV_VERSION` in `.env.test` and `.env.prod`** to the target version. A stale value here installs the wrong core (an rc), which then blocks the `api` plugin and 404s admin.
+   - **Bump `GRAV_VERSION` in `.env.test` and `.env.prod`** to the target version. A stale value here installs the wrong core (an rc), which then blocks the `api` plugin and 404s admin. This governs fresh **remote** installs only.
+   - **If the core version is changing, upgrade the local dev core too** so you prove the change against the target version — bump the hardcoded `grav-admin-v<ver>.zip` URL in `Dockerfile`, `docker compose build grav`, then `docker rm -f intotheeast_grav && docker compose up -d grav`. The local core is baked into the image, so `.env GRAV_VERSION` does *not* touch it and an in-container `gpm self-upgrade` is non-durable. See `docs/solutions/tooling-decisions/upgrade-local-grav-core-rebuild-docker-image.md`.
 2. `make build-assets` if you touched `js/src/*` (never hand-edit the bundled `js/*.js`).
 3. Run the dev server (`docker compose … up`) and the Playwright suite.
 4. Pre-flight assertions: