feat: resolve Phase 1 contract requests and compose every feature

Contracts and core:
- Feature gains auth and stop; FeatureFactory; core composeServer builds the
  context, runs the factories, then the job queue from the union of their jobs
  (R8/R14). startServer uses it; main.ts composes learner, import, studio, AI.
- AppConfig/loadConfig own the layout and settings: courseDirs include
  <dataDir>/courses and <dataDir>/worktrees, studioReposDir, cacheDir,
  importRoots, uploadMaxMb, aiAllowedBaseUrls, transcribeUrl, python.
  resolveConfig derives the same for tests; cachePaths shares the importer's
  cache layout.
- canView: the global author role views every course (R14); the learner,
  studio and AI packages all call it.
- migrate(db, packages): core first, then packages in name order.
- Media: nosniff on every response, a sandbox CSP on svg/html/js; a Range on
  an empty file is 416.
- courseUrl/lessonUrl and the lesson route patterns live in @stc/contracts.

Packages:
- import, studio and AI read AppConfig instead of process.env; the importer
  refuses ids used by studio/repos.
- learner migrations run through core migrate; library covers fall back to
  the importer's cached candidate behind a canView-checked route.
- studio preview renders through the learner LessonView (anchors honoured,
  draft URLs); AI drafts go to the studio draft branch for studio courses (as
  the requesting user) and to <dataDir>/drafts otherwise, and the generator
  page says which.

Web: tsconfig paths for @stc/<feature>/web browser entries; features.ts
imports them by package name; nav.roles hides links by role.

Tests: compose, config, canView, media headers, migrations order, covers,
preview, nav, SPA bundle without server code, and an end-to-end flow on
SQLite and Postgres.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/server/test/server.test.ts

@@ -1,5 +1,7 @@
 import { afterAll, beforeAll, expect, test } from "bun:test";
-import { resolve } from "node:path";
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join, resolve } from "node:path";
 import { loadConfig } from "@stc/core";
 import { startServer } from "../src/main";
 
@@ -7,7 +9,7 @@ let s: Awaited<ReturnType<typeof startServer>>;
 let base: string;
 beforeAll(async () => {
   const config = loadConfig({
-    STC_PORT: "0", STC_DATABASE_URL: "sqlite://:memory:", STC_SECRET: "t",
+    STC_PORT: "0", STC_DATABASE_URL: "sqlite://:memory:", STC_SECRET: "t", STC_DATA_DIR: mkdtempSync(join(tmpdir(), "stc-server-")),
     STC_COURSE_DIRS: resolve(import.meta.dir, "../../../fixtures/courses"),
   });
   s = await startServer(config, []);