Stage 8: UI social/account/history surfaces

Wire the deferred Stage 7 surfaces end-to-end (UI -> gateway transcode ->
backend REST -> existing domain services): friends (incl. one-time friend
codes), per-user blocks, friend-game invitations, profile editing + email
binding, the statistics screen, and the in-game history + GCG export.

Friends gain two add paths (interview decision, a deliberate plan change):
one-time 6-digit codes (friend_codes table, 12h TTL, single-use, rate-limited
redeem); and play-gated requests (shared game required) where an explicit
decline is permanent, an ignored request lapses after 30 days, and a code
bypasses a decline. Migration 00006 widens friendships_status_chk and adds
friend_codes.

Lobby notification badge is poll + push: a new generic `notify` event drives
it live; the client polls on open/focus. Language stays a single Settings
control that writes through to the durable account's preferred_language. GCG
export is finished-only (game.ErrGameActive) and shares/downloads the .gcg file.

Tests: backend unit + inttest (friend gate/decline/code, ListInvitations,
GetStats, GCG gate), gateway transcode round-trips + notify constructor, UI
vitest (codecs, win-rate, share choice) + Playwright social specs. Docs: PLAN
(Stage 8 done + refinements + TODO-5), ARCHITECTURE, FUNCTIONAL(+ru), UI_DESIGN,
TESTING, module READMEs.

backend/internal/server/handlers_blocks.go

@@ -0,0 +1,76 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+// The /api/v1/user/blocks/* handlers wire the per-user block list (Stage 8). A block
+// is mutual in effect (the social checks apply it both ways) and severs any
+// friendship between the pair. They reuse the friend handlers' targetIDRequest and
+// account-ref resolution.
+
+// blockListDTO is the accounts the caller has blocked.
+type blockListDTO struct {
+	Blocked []accountRefDTO `json:"blocked"`
+}
+
+// handleBlock blocks the body-supplied account.
+func (s *Server) handleBlock(c *gin.Context) {
+	uid, ok := userID(c)
+	if !ok {
+		abortBadRequest(c, "missing identity")
+		return
+	}
+	var req targetIDRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		abortBadRequest(c, "invalid request body")
+		return
+	}
+	target, ok := parseUUIDField(req.AccountID)
+	if !ok {
+		abortBadRequest(c, "invalid account id")
+		return
+	}
+	if err := s.social.Block(c.Request.Context(), uid, target); err != nil {
+		s.abortErr(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, okResponse{OK: true})
+}
+
+// handleUnblock removes the caller's block on the :id account.
+func (s *Server) handleUnblock(c *gin.Context) {
+	uid, ok := userID(c)
+	if !ok {
+		abortBadRequest(c, "missing identity")
+		return
+	}
+	target, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		abortBadRequest(c, "invalid account id")
+		return
+	}
+	if err := s.social.Unblock(c.Request.Context(), uid, target); err != nil {
+		s.abortErr(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, okResponse{OK: true})
+}
+
+// handleListBlocks returns the accounts the caller has blocked.
+func (s *Server) handleListBlocks(c *gin.Context) {
+	uid, ok := userID(c)
+	if !ok {
+		abortBadRequest(c, "missing identity")
+		return
+	}
+	ids, err := s.social.ListBlocks(c.Request.Context(), uid)
+	if err != nil {
+		s.abortErr(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, blockListDTO{Blocked: s.accountRefs(c.Request.Context(), ids)})
+}