feat(api): tiered cumulative quota + self-service registration

Anonymous callers get a free cumulative quota (1000 calls per IP); once
exhausted they get 403 quota_exhausted and must register. Public users can
self-register (email+password) to obtain a higher-quota API key, view usage,
and regenerate the key. Quota counters live in Redis; the public API stays
read-only except for the registration writes.

- migration 0011: app_user table + api_key.quota_total + 'registered' tier
- ratelimit: IncrTotal/TotalUsed/CopyTotal lifetime counters
- middleware: enforce cumulative quota + X-Quota-* headers
- store: RegisterUser/Authenticate/RegenerateKey (bcrypt)
- handlers: POST /api/v1/register, /account, /account/regenerate
- admin: quota_total column + registered tier
- public: 'API 密钥' account page + API docs quota section

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

api/internal/handler/account.go

@@ -0,0 +1,128 @@
+package handler
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"regexp"
+	"strings"
+
+	"github.com/baicai2026-baicai/goods/api/internal/store"
+)
+
+// emailRe is a deliberately permissive sanity check; real validation is the
+// unique constraint plus the user being able to receive their own key.
+var emailRe = regexp.MustCompile(`^[^@\s]+@[^@\s]+\.[^@\s]+$`)
+
+const minPasswordLen = 8
+
+type credentials struct {
+	Email    string `json:"email"`
+	Password string `json:"password"`
+}
+
+func decodeCredentials(w http.ResponseWriter, r *http.Request) (credentials, bool) {
+	var c credentials
+	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&c); err != nil {
+		writeError(w, r, http.StatusBadRequest, "invalid_body", "请求格式无效")
+		return credentials{}, false
+	}
+	c.Email = strings.TrimSpace(c.Email)
+	if !emailRe.MatchString(c.Email) {
+		writeError(w, r, http.StatusBadRequest, "invalid_email", "邮箱格式无效")
+		return credentials{}, false
+	}
+	if len(c.Password) < minPasswordLen {
+		writeError(w, r, http.StatusBadRequest, "weak_password", "密码至少需要 8 位")
+		return credentials{}, false
+	}
+	return c, true
+}
+
+// keyResponse is returned whenever a fresh plaintext key is issued; the key is
+// shown exactly once and cannot be recovered afterwards.
+type keyResponse struct {
+	Email           string `json:"email"`
+	APIKey          string `json:"api_key"`
+	KeyPrefix       string `json:"key_prefix"`
+	RateLimitPerMin int    `json:"rate_limit_per_min"`
+	QuotaTotal      int64  `json:"quota_total"`
+}
+
+// Register creates an account and issues its first API key. POST {email, password}.
+func (h *Handler) Register(w http.ResponseWriter, r *http.Request) {
+	c, ok := decodeCredentials(w, r)
+	if !ok {
+		return
+	}
+	key, acct, err := h.store.RegisterUser(r.Context(), c.Email, c.Password, h.regRatePerMin, h.regQuotaTotal)
+	if errors.Is(err, store.ErrEmailTaken) {
+		writeError(w, r, http.StatusConflict, "email_taken", "该邮箱已注册，请直接登录查看或重置密钥")
+		return
+	}
+	if h.handleErr(w, r, err) {
+		return
+	}
+	writeJSON(w, http.StatusCreated, keyResponse{
+		Email:           acct.Email,
+		APIKey:          key,
+		KeyPrefix:       acct.KeyPrefix,
+		RateLimitPerMin: acct.RateLimitPerMin,
+		QuotaTotal:      acct.QuotaTotal,
+	})
+}
+
+// AccountInfo verifies credentials and returns the account's key metadata plus
+// cumulative usage. POST {email, password}. The plaintext key is not returned.
+func (h *Handler) AccountInfo(w http.ResponseWriter, r *http.Request) {
+	c, ok := decodeCredentials(w, r)
+	if !ok {
+		return
+	}
+	acct, err := h.store.Authenticate(r.Context(), c.Email, c.Password)
+	if errors.Is(err, store.ErrNotFound) {
+		writeError(w, r, http.StatusUnauthorized, "invalid_credentials", "邮箱或密码错误")
+		return
+	}
+	if h.handleErr(w, r, err) {
+		return
+	}
+	used := h.limiter.TotalUsed(r.Context(), acct.KeyID)
+	remaining := acct.QuotaTotal - used
+	if remaining < 0 {
+		remaining = 0
+	}
+	writeJSON(w, http.StatusOK, map[string]any{
+		"email":              acct.Email,
+		"key_prefix":         acct.KeyPrefix,
+		"rate_limit_per_min": acct.RateLimitPerMin,
+		"quota_total":        acct.QuotaTotal,
+		"quota_used":         used,
+		"quota_remaining":    remaining,
+	})
+}
+
+// RegenerateKey revokes the account's current key and issues a new one, carrying
+// over cumulative usage so the quota cannot be reset. POST {email, password}.
+func (h *Handler) RegenerateKey(w http.ResponseWriter, r *http.Request) {
+	c, ok := decodeCredentials(w, r)
+	if !ok {
+		return
+	}
+	key, acct, oldKeyID, err := h.store.RegenerateKey(r.Context(), c.Email, c.Password, h.regRatePerMin, h.regQuotaTotal)
+	if errors.Is(err, store.ErrNotFound) {
+		writeError(w, r, http.StatusUnauthorized, "invalid_credentials", "邮箱或密码错误")
+		return
+	}
+	if h.handleErr(w, r, err) {
+		return
+	}
+	h.limiter.CopyTotal(r.Context(), oldKeyID, acct.KeyID)
+	writeJSON(w, http.StatusOK, keyResponse{
+		Email:           acct.Email,
+		APIKey:          key,
+		KeyPrefix:       acct.KeyPrefix,
+		RateLimitPerMin: acct.RateLimitPerMin,
+		QuotaTotal:      acct.QuotaTotal,
+	})
+}