Index-backed search, /api surfaces, image-only PDF detection

search now queries the Postgres index and states its freshness in every
result, with fresh=true bypassing it for a live crawl — the agent can
always get current data rather than being quietly misled by a stale
index. Adds refresh_index (per-course by default; a full crawl is ~270
requests), what_changed (generation diff — the API has no changed-since
filter of any kind), and index_status.

/api gives the CLI its backend behind the same bearer token as /mcp:
GET /manifest (cursor + per-file status), GET /files/:id (served from
the mirror with Range support, falling back to a live proxy for files
too large to mirror), GET /status, POST /refresh. Bytes go over plain
HTTP rather than MCP because base64 in JSON-RPC costs a third more and
buffers whole files. An unresolvable manifest cursor returns 409 rather
than silently meaning "everything is new", so a client cannot be tricked
into a full re-download.

Verified end to end against the live instance and a real Postgres:
crawl -> index -> German FTS -> manifest -> ranged download, with 401
on missing token, 400 on a malformed id, and 429 on a too-soon refresh.

Two findings worth recording. The build silently omitted the .sql
migrations from dist, which the store's graceful degradation turned into
"running without the index" rather than a crash — now copied by a build
step. And 3 of 4 sampled course PDFs have no embedded fonts at all: they
are scans, so extraction legitimately yields nothing. That is now
detected and reported as image-only with OCR named as the missing piece,
instead of an indistinguishable "0 characters". It revises the roadmap's
"OCR not needed" note, which held for reading images but not for
indexing them.

49 tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/copy-assets.mjs

@@ -0,0 +1,17 @@
+#!/usr/bin/env node
+/**
+ * Copies non-TypeScript assets into dist/.
+ *
+ * tsc emits only .js, so the .sql migrations would be missing at runtime — and
+ * the failure is quiet, because the store degrades to live-only mode rather
+ * than crashing. Keeping this in the build avoids that confusing outcome.
+ */
+import { cp, mkdir } from 'node:fs/promises';
+
+const assets = [['src/store/migrations', 'dist/store/migrations']];
+
+for (const [from, to] of assets) {
+	await mkdir(to, { recursive: true });
+	await cp(from, to, { recursive: true });
+	console.log(`copied ${from} -> ${to}`);
+}