feat(telegram): bot support relay — per-user forum topics

Users who DM the bot anything but /start are relayed into a private
forum supergroup, one topic per user. Operators (the chat's admins)
reply in the topic and the bot copies it back to the user; an info card
opening each topic carries a Block/Unblock toggle and a Clear button.
State is a small JSON file on a new /data volume — the bot host has no
database. Off by default (TELEGRAM_SUPPORT_CHAT_ID=0): the prod bot is
unchanged until the operator sets the chat id and adds the bot as a
forum admin.

- internal/support: concurrency-safe JSON store (topic map, block list,
  relayed message ids) with field-targeted mutators and atomic save
- bot/support.go: relay both ways via copyMessage, short-TTL admin
  cache, callback buttons, per-user topic-create lock, loop guard
  (skip the bot's own posts), reopen a deleted topic on the next message
- config + compose + CI/prod-deploy: TELEGRAM_SUPPORT_CHAT_ID per
  contour + TELEGRAM_SUPPORT_STATE_DIR; bot-state named volume; /data
  pre-owned by UID 65532 so a fresh volume is writable under distroless
- docs: ARCHITECTURE §15 + decision record, FUNCTIONAL (+ru), README

platform/telegram/internal/config/config.go

@@ -42,6 +42,16 @@ type BotConfig struct {
 	// (TELEGRAM_CHAT_ID, optional; 0 disables chat gating). The bot must be an admin
 	// there with the "Ban users" right, and "chat_member" in its allowed updates.
 	ChatID int64
+	// SupportChatID is the chat id of the private forum supergroup the bot relays
+	// direct user messages into — one forum topic per user — and reads operator
+	// replies from (TELEGRAM_SUPPORT_CHAT_ID, optional; 0 disables the support relay).
+	// The bot must be an administrator there with the manage-topics and
+	// delete-messages rights. Distinct from ChatID (the moderated discussion chat).
+	SupportChatID int64
+	// SupportStateDir is the directory holding the support relay's JSON state file
+	// (TELEGRAM_SUPPORT_STATE_DIR, default /data). It must be writable by the
+	// container user (UID 65532) and backed by a persistent volume.
+	SupportStateDir string
 	// PromoBotToken is the API token of the optional standalone promo bot run in this
 	// container — a second bot whose only job is to answer /start with a button that
 	// opens the main bot's Mini App (TELEGRAM_PROMO_BOT_TOKEN, optional; empty disables
@@ -135,6 +145,7 @@ func LoadBot() (BotConfig, error) {
 		PromoBotToken:     os.Getenv("TELEGRAM_PROMO_BOT_TOKEN"),
 		BotUsername:       strings.TrimPrefix(os.Getenv("TELEGRAM_BOT_USERNAME"), "@"),
 		BotLinkURL:        os.Getenv("TELEGRAM_BOT_LINK"),
+		SupportStateDir:   envOr("TELEGRAM_SUPPORT_STATE_DIR", "/data"),
 		LogLevel:          envOr("TELEGRAM_LOG_LEVEL", "info"),
 		BotLink: BotLinkClientConfig{
 			GatewayAddr: os.Getenv("TELEGRAM_GATEWAY_ADDR"),
@@ -152,6 +163,9 @@ func LoadBot() (BotConfig, error) {
 	if cfg.ChatID, err = envInt64("TELEGRAM_CHAT_ID", 0); err != nil {
 		return BotConfig{}, err
 	}
+	if cfg.SupportChatID, err = envInt64("TELEGRAM_SUPPORT_CHAT_ID", 0); err != nil {
+		return BotConfig{}, err
+	}
 	if cfg.SendRatePerSecond, err = envInt("TELEGRAM_SEND_RATE_PER_SECOND", defaultSendRatePerSecond); err != nil {
 		return BotConfig{}, err
 	}