feat(embedding): 嵌入（n-gram 哈希向量 + 关键词 FTS + OpenAI 兼容 API 钩子 + Manager 选择）

internal/runtime/embedding/manager.go

@@ -0,0 +1,43 @@
+package embedding
+
+import (
+	"context"
+	"strings"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/config"
+)
+
+// Manager selects the runtime embedder based on configuration and exposes it
+// through a single Embedder handle.
+//
+// When config.EmbeddingConfig.APIURL is set, the semantic APIEmbedder is
+// chosen; otherwise the built-in NGramEmbedder is used. In both cases the
+// caller receives a consistent Embedder that is safe for concurrent use.
+//
+// It is the integration point described in DevDocs/design/04-运行时.md §7: the
+// API path is a real semantic-vector enhancement, while the n-gram path keeps
+// the runtime zero-dependency and offline.
+type Manager struct {
+	embedder Embedder
+}
+
+// New builds a Manager for cfg and selects the embedder. When cfg.APIURL is set
+// (ignoring surrounding whitespace), an APIEmbedder is used; otherwise an
+// NGramEmbedder with the default dimension.
+func New(cfg config.EmbeddingConfig) *Manager {
+	var embedder Embedder
+	if strings.TrimSpace(cfg.APIURL) != "" {
+		embedder = NewAPI(cfg)
+	} else {
+		embedder = NewNGram(defaultNGramDim)
+	}
+	return &Manager{embedder: embedder}
+}
+
+// Embedder returns the selected embedder.
+func (m *Manager) Embedder() Embedder { return m.embedder }
+
+// Embed is a convenience pass-through to the selected embedder.
+func (m *Manager) Embed(ctx context.Context, texts []string) ([]Vector, error) {
+	return m.embedder.Embed(ctx, texts)
+}