feat(TRUEREF-0007): implement pluggable embedding generation and vector storage

Add EmbeddingProvider interface with OpenAI-compatible, local (optional
@xenova/transformers via dynamic import), and Noop (FTS5-only fallback)
implementations. EmbeddingService batches requests and persists Float32Array
blobs to snippet_embeddings. GET/PUT /api/v1/settings/embedding endpoints
read and write embedding config from the settings table.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/server/embeddings/factory.ts

@@ -0,0 +1,52 @@
+/**
+ * Factory — create an EmbeddingProvider from a persisted EmbeddingConfig.
+ */
+
+import type { EmbeddingProvider } from './provider.js';
+import { NoopEmbeddingProvider } from './provider.js';
+import { OpenAIEmbeddingProvider } from './openai.provider.js';
+import { LocalEmbeddingProvider } from './local.provider.js';
+
+export interface EmbeddingConfig {
+	provider: 'openai' | 'local' | 'none';
+	openai?: {
+		baseUrl: string;
+		apiKey: string;
+		model: string;
+		dimensions?: number;
+		maxBatchSize?: number;
+	};
+}
+
+/** The settings table key used to persist the embedding configuration. */
+export const EMBEDDING_CONFIG_KEY = 'embedding_config';
+
+/**
+ * Construct the appropriate EmbeddingProvider for the given config.
+ * Falls back to NoopEmbeddingProvider for unknown or missing providers.
+ */
+export function createProviderFromConfig(config: EmbeddingConfig): EmbeddingProvider {
+	switch (config.provider) {
+		case 'openai': {
+			if (!config.openai) {
+				throw new Error('OpenAI provider selected but no openai config provided.');
+			}
+			return new OpenAIEmbeddingProvider(config.openai);
+		}
+		case 'local': {
+			return new LocalEmbeddingProvider();
+		}
+		case 'none':
+		default:
+			return new NoopEmbeddingProvider();
+	}
+}
+
+/**
+ * Return a default (noop) config when nothing has been stored yet.
+ */
+export function defaultEmbeddingConfig(): EmbeddingConfig {
+	return { provider: 'none' };
+}
+
+export type { EmbeddingProvider };