feat(auth): data-driven password requirement checkers

GET /api/auth/password-rules (public, pre-auth) exposes the ACTIVE
complexity config from the settings registry; password_validation.ts
now fetches it and generates the checklist rows per active rule —
inactive requirements no longer linger as fake tasks, and the min
length mirrors the admin's setting instead of a hardcoded 8.

Surfaces: register, setup, admin create-user (Users page), profile
password change (self + admin variants, now gated on checklist pass;
misleading minlength=6 dropped — the server was always the enforcer).

Verified live: flip min_length=12 / number+special off via the
settings API → endpoint + register/profile/admin checklists re-render
row-for-row; enforcement follows (short rejected, rule-valid accepted
without digits/specials); restore defaults → checklists return.

internal/router/auth.go

@@ -12,6 +12,7 @@ func registerAuthRoutes(cfg *Config, rateLimitMiddleware echo.MiddlewareFunc) {
 	// Auth routes (no auth required, but rate limited)
 	e.POST("/api/auth/register", rateLimitMiddleware(cfg.AuthHandler.Register))
 	e.POST("/api/auth/login", rateLimitMiddleware(cfg.AuthHandler.Login))
+	e.GET("/api/auth/password-rules", cfg.AuthHandler.GetPasswordRules)
 
 	// JWT middleware for protected routes
 	jwtMiddleware := createJWTMiddleware(cfg)