docs: finalize documentation to the production state

The project is live in production, so the staged-development scaffolding is removed.

- Delete the staged trackers PLAN.md and PRERELEASE.md.
- Rewrite CLAUDE.md: drop the per-stage workflow; codify the ongoing development
  principles (How we work) and the production model (Branching, CI & production):
  manual prod-deploy / prod-rollback, semver release tags, Ansible provisioning,
  expand-contract migrations.
- De-stage the living docs (README, ARCHITECTURE, TESTING, deploy/ansible, loadtest,
  platform/telegram READMEs) and the docker-compose tuning comments: drop the
  Stage N / R1-R7 / pre-release labels, keep every number and rationale, and fix the
  now-dangling PLAN.md / PRERELEASE.md references to describe the current state.
- Reword stale 'later stage' Go doc comments for subsystems that have shipped.

docs/ARCHITECTURE.md

@@ -2,10 +2,8 @@
 
 Source of truth for the platform architecture, transport, security model and
 cross-service contracts. User-visible behaviour per domain lives in
-[`FUNCTIONAL.md`](FUNCTIONAL.md); the staged build order lives in
-[`../PLAN.md`](../PLAN.md). This document always describes the **current**
-design, not the history of how it was reached. Sections describing
-not-yet-implemented components are marked *(planned)*.
+[`FUNCTIONAL.md`](FUNCTIONAL.md). This document always describes the **current**
+design, not the history of how it was reached.
 
 ## 1. Overview
 
@@ -1107,7 +1105,7 @@ Two contours, two secret/variable prefixes (`TEST_` / `PROD_`):
   **`prod-rollback`** workflow re-deploys any prior release tag (blank input = the previous
   deployed version, tracked on the host) over the same rolling, health-gated path — image-only,
   no DB migration. The main host is
-  intentionally **launch-sized** (2 vCPU / 1.9 GiB): the prod overlay trims the R7 limits
+  intentionally **launch-sized** (2 vCPU / 1.9 GiB): the prod overlay trims the baseline limits
   (`GOMAXPROCS=2`, smaller caps, 7d Prometheus retention) and a **node_exporter** feeds
   host-memory metrics to Grafana so it can be resized reactively as players arrive.
   `GATEWAY_ABUSE_BAN_ENABLED=true` in prod (the per-IP ban is meaningful only with real