feat(TRUEREF-0009-0010): implement indexing pipeline job queue and public REST API

- SQLite-backed job queue with sequential processing and startup recovery
- Atomic snippet replacement in single transaction
- context7-compatible GET /api/v1/libs/search and GET /api/v1/context
- Token budget limiting and JSON/txt response format support
- CORS headers on all API routes via SvelteKit handle hook
- Library ID parser supporting /owner/repo and /owner/repo/version

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

src/lib/server/api/token-budget.ts

@@ -0,0 +1,36 @@
+/**
+ * Token budget selection for context responses.
+ *
+ * Implements a greedy selection algorithm: snippets are added in ranked order
+ * until adding the next snippet would exceed the token budget.
+ */
+
+import type { Snippet } from '$lib/types';
+
+/**
+ * Select snippets from a ranked list up to a maximum token budget.
+ *
+ * Snippets are evaluated in order. A snippet is included when its token count
+ * does not push the running total past `maxTokens`. The loop halts at the
+ * first snippet that would exceed the budget.
+ *
+ * @param snippets  - Ranked list of snippets (best first).
+ * @param maxTokens - Inclusive upper bound on total token count.
+ * @returns The largest prefix of `snippets` whose combined token count
+ *          does not exceed `maxTokens`.
+ */
+export function selectSnippetsWithinBudget(snippets: Snippet[], maxTokens: number): Snippet[] {
+	const selected: Snippet[] = [];
+	let usedTokens = 0;
+
+	for (const snippet of snippets) {
+		if (usedTokens + (snippet.tokenCount ?? 0) > maxTokens) break;
+		selected.push(snippet);
+		usedTokens += snippet.tokenCount ?? 0;
+	}
+
+	return selected;
+}
+
+/** Default token budget when the caller does not specify `tokens`. */
+export const DEFAULT_TOKEN_BUDGET = 10_000;