feat(mcpedia): Phase 2 — semantic + hybrid search, tRPC/Hono API

- @mcpedia/embeddings: OpenRouter provider (9router /v1, encoding_format float),
  chunkText + embedChunks; EMBED_DIM=2048
- document_chunks table (real[] embedding) — pgvector NOT available on shared
  imrnes Postgres, so cosine is computed in-app (KB-scale fine); pgvector deferred
- indexer: chunk + embed + upsert per document
- @mcpedia/search: semanticSearch (cosine) + hybridSearch (FTS+cosine RRF)
- apps/api: Hono + tRPC v11 (6 procedures), serve on :4020
- MCP: semantic_search + hybrid_search tools (6 total)
- web: keyword/hybrid toggle; .env.example + README + PHASES updated

packages/embeddings/src/provider.ts

@@ -0,0 +1,82 @@
+import {
+  EMBED_API_KEY,
+  EMBED_BASE_URL,
+  EMBED_MODEL,
+} from "@mcpedia/config";
+
+export interface EmbeddingProvider {
+  /** Embed a batch of texts into vectors of fixed dimension. */
+  embed(texts: string[]): Promise<number[][]>;
+  readonly model: string;
+  readonly dimensions: number;
+}
+
+/** Pinned embedding dimension for the configured OpenRouter model. */
+export const EMBED_DIM = 2048;
+
+/**
+ * OpenRouter embeddings provider (we route through 9router's OpenAI-compatible
+ * /v1 endpoint). `encoding_format: "float"` is REQUIRED — the Nvidia-backed
+ * model rejects base64.
+ */
+export class OpenRouterEmbeddingProvider implements EmbeddingProvider {
+  readonly model: string;
+  private readonly baseUrl: string;
+  private readonly apiKey: string;
+
+  constructor(opts?: {
+    baseUrl?: string;
+    apiKey?: string;
+    model?: string;
+  }) {
+    this.baseUrl = (opts?.baseUrl ?? EMBED_BASE_URL).replace(/\/$/, "");
+    this.apiKey = opts?.apiKey ?? EMBED_API_KEY;
+    this.model = opts?.model ?? EMBED_MODEL;
+    if (!this.baseUrl || !this.apiKey || !this.model) {
+      throw new Error(
+        "OpenRouterEmbeddingProvider: missing EMBED_BASE_URL / EMBED_API_KEY / EMBED_MODEL",
+      );
+    }
+  }
+
+  get dimensions(): number {
+    return EMBED_DIM;
+  }
+
+  async embed(texts: string[]): Promise<number[][]> {
+    if (texts.length === 0) return [];
+    const res = await fetch(`${this.baseUrl}/embeddings`, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+        Authorization: `Bearer ${this.apiKey}`,
+      },
+      body: JSON.stringify({
+        model: this.model,
+        input: texts,
+        encoding_format: "float",
+      }),
+    });
+    if (!res.ok) {
+      const body = await res.text().catch(() => "");
+      throw new Error(
+        `embedding request failed (${res.status}): ${body.slice(0, 300)}`,
+      );
+    }
+    const json = (await res.json()) as {
+      data?: { embedding: number[] }[];
+    };
+    const data = json.data;
+    if (!data || data.length !== texts.length) {
+      throw new Error(
+        `embedding response mismatch: expected ${texts.length}, got ${data?.length ?? 0}`,
+      );
+    }
+    return data.map((d) => d.embedding);
+  }
+}
+
+/** Default singleton provider. */
+export function createEmbeddingProvider(): EmbeddingProvider {
+  return new OpenRouterEmbeddingProvider();
+}