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.

backend/cmd/backend/main.go

@@ -3,8 +3,8 @@
 // loads the dictionaries into the engine registry, warms the session cache,
 // constructs the game domain and starts its turn-timeout sweeper, constructs the
 // lobby and social domains, then serves the HTTP listener with the infrastructure
-// probes and the /api/v1 route-group skeleton. Domain HTTP endpoints are added
-// with the gateway in a later stage described in PLAN.md.
+// probes and the /api/v1 route group, behind which the domains expose their HTTP
+// endpoints to the gateway.
 package main
 
 import (

backend/internal/engine/decode.go

@@ -21,7 +21,7 @@ const (
 	// ActionResign abandons the game.
 	ActionResign
 	// ActionTimeout is the auto-resignation a missed turn becomes; recorded by
-	// the game domain in a later stage, never produced by the engine itself.
+	// the game domain, never produced by the engine itself.
 	ActionTimeout
 )
 

backend/internal/engine/engine.go

@@ -10,7 +10,7 @@
 // characters (see decode.go and docs/ARCHITECTURE.md §9.1), so archived games
 // replay independently of any dictionary. Second, the engine owns rules and
 // scoring only: turn scheduling, the 24-hour timeout, persistence and transport
-// belong to the game domain in a later stage.
+// belong to the game domain.
 package engine
 
 import (

backend/internal/engine/registry.go

@@ -31,7 +31,7 @@ type entry struct {
 // Registry holds the dictionaries resident in memory, addressed by variant and
 // dictionary version, and the solvers built over them. Several versions of a
 // variant may be resident at once; a game pins the version it started on. The
-// admin reload flow (a later stage) registers a new version through Load.
+// admin reload flow registers a new version through Load.
 // Registry is safe for concurrent use.
 type Registry struct {
 	mu      sync.RWMutex

backend/internal/game/doc.go

@@ -16,5 +16,5 @@
 // word-check tool with complaint capture, per-player game state, history and GCG
 // export, and the per-game turn-timeout sweeper that auto-resigns an overdue
 // player (honouring their daily away window). The HTTP surface that fronts these
-// operations is added with the gateway in a later stage.
+// operations is exposed to the gateway.
 package game

backend/internal/game/types.go

@@ -105,7 +105,7 @@ const MaxActiveQuickGames = 10
 const aiPlayerName = "AI"
 
 // CreateParams describes a new game. Seats lists the seated accounts in turn
-// order (seat 0 moves first); lobby/matchmaking assembles it in a later stage.
+// order (seat 0 moves first); lobby/matchmaking assembles it.
 type CreateParams struct {
 	Variant        engine.Variant
 	Seats          []uuid.UUID

backend/internal/inttest/email_test.go

@@ -62,7 +62,7 @@ func TestEmailConfirmFlow(t *testing.T) {
 }
 
 // TestEmailAlreadyTakenByAnotherAccount refuses to bind an email confirmed by a
-// different account (merge is a later stage).
+// different account (combining two accounts is the separate link/merge flow).
 func TestEmailAlreadyTakenByAnotherAccount(t *testing.T) {
 	ctx := context.Background()
 	store := account.NewStore(testDB)

backend/internal/server/server.go

@@ -1,10 +1,10 @@
 // Package server wires the backend's HTTP listener: the gin engine, its route
 // groups, the per-request telemetry middleware and the start/stop lifecycle.
 //
-// The /api/v1 route groups (public, user, internal, admin) are created here so
-// later stages attach their endpoints to a stable structure; the /user group
-// requires the X-User-ID identity header. The probes /healthz (liveness) and
-// /readyz (database + session-cache readiness) are unauthenticated.
+// The /api/v1 route groups (public, user, internal, admin) attach their endpoints
+// to a stable structure; the /user group requires the X-User-ID identity header.
+// The probes /healthz (liveness) and /readyz (database + session-cache readiness)
+// are unauthenticated.
 package server
 
 import (
@@ -245,7 +245,7 @@ func (s *Server) Invitations() *lobby.InvitationService { return s.invitations }
 func (s *Server) Emails() *account.EmailService { return s.emails }
 
 // Handler returns the underlying HTTP handler. It lets tests drive the server
-// without binding a socket and lets later stages compose the backend behind
+// without binding a socket and lets callers compose the backend behind
 // another listener.
 func (s *Server) Handler() http.Handler { return s.http.Handler }
 

backend/internal/session/service.go

@@ -8,8 +8,7 @@ import (
 )
 
 // Service mints, resolves, and revokes sessions over the store and the
-// write-through cache. The gateway is its only caller (from a later stage); the
-// HTTP surface is wired then.
+// write-through cache. The gateway is its only caller.
 type Service struct {
 	store *Store
 	cache *Cache

backend/internal/social/social.go

@@ -3,8 +3,8 @@
 // in as a message kind. It owns the friendships, blocks and chat_messages tables,
 // reads the account-level block toggles through account.Store, and gates chat and
 // nudge on game state through a GameReader so it never imports the engine. The
-// live delivery of chat and nudges (push / in-app stream) belongs to the gateway
-// in a later stage; this package only persists and reads them.
+// live delivery of chat and nudges (push / in-app stream) belongs to the gateway;
+// this package only persists and reads them.
 package social
 
 import (