feat(deploy): add stage tier — park-buzi as the staging booth

Model the staging-vs-production split that fleet-deployment-komodo flagged as open.
Three tiers: dev (working, no booth) -> stage (staging booth park-buzi, real-world
test) -> main (production, manual + pinned).

- build-images.yml: trigger on [dev, stage, main]. The tag computation is already
  branch-derived, so :stage / :stage-<sha> build with no other change.
- komodo/resources.toml: park-buzi now branch=stage + TAG=stage-<sha> (pinned;
  no webhook even on staging). BACKUP_KEY already wired as a per-booth secret.
- komodo/README.md: a Promotion (dev->stage->main) section; per-booth secret list
  now includes backup_key; hard-rule #1 generalised to pinned <branch>-<sha>.
- wiki: fleet-deployment-komodo open-item resolved + a Promotion-tiers table;
  deploy-trigger choice generalised; container-deployment tag list gains :stage.

Promotion is a merge: when dev is ready, merge dev->stage, CI builds the image,
bump TAG=stage-<sha> in resources.toml, deploy from Core. stage is branched from
dev HEAD so the first real-world test carries the full current app. Per-booth
secrets must pre-exist in Core; migrations run at boot so a promotion auto-migrates
the staging ledger (where a bad migration is caught before production).

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

wiki/decisions/container-deployment.md

@@ -35,8 +35,10 @@ The **desktop** app stays on its own tag-only `release.yml` (Tauri installers),
 ## Branch-aware (the user's hard requirement)
 
 - **Image tags = branch + short SHA.** A push to `dev` builds `…/parking-server:dev` +
-  `…/parking-server:dev-<sha>`; `main` builds `:main` + `:main-<sha>`. The moving branch tag is the
-  deploy pointer; the branch-SHA tag is the immutable record. Same for `parking-vision`.
+  `…/parking-server:dev-<sha>`; `stage` builds `:stage` + `:stage-<sha>`; `main` builds `:main` +
+  `:main-<sha>`. The moving branch tag is the deploy pointer; the branch-SHA tag is the immutable
+  record. Same for `parking-vision`. (The `stage` tier — the staging booth — was added 2026-06-29;
+  see [[fleet-deployment-komodo]] "Promotion tiers".)
 - **Per-env compose.** A base `docker-compose.yml` + overrides: `docker-compose.dev.yml` (build
   locally, expose ports, `stub` recognizer) and `docker-compose.prod.yml` (pull pinned images,
   `restart: always`, `fast_alpr`, vision kept internal). `REGISTRY`/`TAG` come from env, so a deploy