Stage 16: insert Stage 17 (test-contour verification); renumber prod deploy to 18

- PLAN.md: new Stage 17 "Test-contour verification & defect fixes" (exercise the
  deployed contour end-to-end and fix what it surfaces — connector liveness check,
  path-conditional CI); the former prod-deploy stage becomes Stage 18.
- Renumber every "Stage 17" prod-deploy reference to "Stage 18" across docs,
  compose, Caddyfile, ci.yaml and CLAUDE.md; the post-Stage-14 split range is now
  "Stages 15–18".

.gitea/workflows/ci.yaml

@@ -9,7 +9,7 @@ name: CI
 # `development` or `master` (the full test suite — the merge gate) and on a push
 # to `development` (after a merge). The deploy job runs only for `development`
 # (PR or merge), so a PR into `master` is test-only; the prod deploy is a manual
-# workflow (Stage 17).
+# workflow (Stage 18).
 #
 # Console output is kept plain (NO_COLOR + `docker compose --ansi never` +
 # `--progress plain`) so the Gitea logs stay readable.
@@ -176,7 +176,7 @@ jobs:
           TELEGRAM_GAME_CHANNEL_ID_EN: ${{ vars.TEST_TELEGRAM_GAME_CHANNEL_ID_EN }}
           TELEGRAM_GAME_CHANNEL_ID_RU: ${{ vars.TEST_TELEGRAM_GAME_CHANNEL_ID_RU }}
           # The test contour always uses Telegram's test environment — pinned here,
-          # not an operator variable. Stage 17's prod workflow leaves it false.
+          # not an operator variable. Stage 18's prod workflow leaves it false.
           TELEGRAM_TEST_ENV: "true"
           VITE_TELEGRAM_BOT_ID: ${{ vars.TEST_VITE_TELEGRAM_BOT_ID }}
           VITE_TELEGRAM_LINK: ${{ vars.TEST_VITE_TELEGRAM_LINK }}