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.

loadtest/README.md

@@ -1,6 +1,6 @@
 # loadtest — stress harness
 
-Reusable load harness for the pre-release stress pass. It
+Reusable load/stress harness. It
 seeds a large account population with pre-created sessions, drives virtual players
 through the **gateway edge protocol** in realistic games, hammers the rate limiter,
 and prints a trip-report summary. It stays in the repo for repeats.
@@ -107,6 +107,6 @@ gateway→backend connection-pool fix, and the revised sizing — are written up
 
 The harness shares the host CPU with the contour, so its own `scrabble-loadtest`
 container series is read alongside the system under test; capping it with `--cpus`
-keeps the contour's quota. Per-player transports (R7) removed the shared-transport
-artifact that inflated R2's `transport_error`, so the figures reflect the system. A
+keeps the contour's quota. Per-player transports removed the shared-transport
+artifact that previously inflated `transport_error`, so the figures reflect the system. A
 fully isolated ceiling on separate hardware remains future work.