feat: add RelationInsight API and wire H5 relation/profile pages

Second P1 growth engine: compare two profiles, gate full tips behind
deep-access mock payment, and list personal archives on /profile.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/internal/relation/engine.go

@@ -0,0 +1,83 @@
+// Package relation builds 关系理解 content from two birth-based portraits.
+package relation
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/yuxingu/digital-psychology/apps/api/internal/portrait"
+)
+
+// Output is free summary + gated detail.
+type Output struct {
+	Summary map[string]any
+	Detail  map[string]any
+}
+
+// Build compares two profiles' exploration styles (lexicon-safe copy).
+func Build(aBirth, bBirth time.Time, aName, bName string) Output {
+	if aName == "" {
+		aName = "我"
+	}
+	if bName == "" {
+		bName = "TA"
+	}
+	pa := portrait.Build(aBirth, aName)
+	pb := portrait.Build(bBirth, bName)
+	aLabel := str(pa.Summary["headline"])
+	bLabel := str(pb.Summary["headline"])
+	aKeys := strSlice(pa.Summary["keywords"])
+	bKeys := strSlice(pb.Summary["keywords"])
+
+	summary := map[string]any{
+		"title":          "关系理解·基础",
+		"me_style":       aLabel,
+		"other_style":    bLabel,
+		"me_keywords":    aKeys,
+		"other_keywords": bKeys,
+		"diff_one_liner": fmt.Sprintf("%s更偏内在节奏，%s的表达方式不同——差异可以成为互补，而不是对立。", aName, bName),
+		"share_hint":     "了解彼此的沟通方式，查看关系理解",
+	}
+	detail := map[string]any{
+		"title": "相处建议·完整分析",
+		"communication": []string{
+			fmt.Sprintf("%s：先讲清楚事实与需要，再谈感受。", aName),
+			fmt.Sprintf("%s：先确认被听见，再进入方案讨论。", bName),
+			"冲突时约定「复述对方一句」再回应，降低误解。",
+		},
+		"interaction": []string{
+			"用「我观察到…我需要…」代替指责句式。",
+			"每周留一次轻松同步：最近什么在消耗/滋养这段关系。",
+		},
+		"maintenance": []string{
+			"差异标签不是评分，而是协作说明书。",
+			"重要决定前，双方各写三点顾虑再合并。",
+		},
+		"me_behavior":    str(pa.Detail["behavior_pattern"]),
+		"other_behavior": str(pb.Detail["behavior_pattern"]),
+	}
+	return Output{Summary: summary, Detail: detail}
+}
+
+func str(v any) string {
+	s, _ := v.(string)
+	return s
+}
+
+func strSlice(v any) []string {
+	arr, ok := v.([]string)
+	if ok {
+		return arr
+	}
+	raw, ok := v.([]any)
+	if !ok {
+		return nil
+	}
+	out := make([]string, 0, len(raw))
+	for _, x := range raw {
+		if s, ok := x.(string); ok {
+			out = append(out, s)
+		}
+	}
+	return out
+}