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>

packages/feature-learner/test/app.ts

@@ -2,7 +2,7 @@ import { mkdtempSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join, resolve } from "node:path";
 import type { AppConfig, JobQueue, ServerContext } from "@stc/contracts";
-import { createApp } from "@stc/core";
+import { createApp, resolveConfig } from "@stc/core";
 import { createCourseRepository } from "@stc/course-format";
 import type { Db } from "@stc/db";
 import { learnerFeature } from "../src/server/feature";
@@ -13,10 +13,10 @@ export const ORIGIN = "http://localhost:3000";
 const fakeJobs: JobQueue = { enqueue: async () => "j", get: async () => null, list: async () => [] };
 
 export async function makeApp(db: Db, courseDirs: string[] = [FIXTURES]) {
-  const config: AppConfig = {
+  const config: AppConfig = resolveConfig({
     port: 0, databaseUrl: "", dataDir: mkdtempSync(join(tmpdir(), "stc-learner-")), courseDirs,
     secret: "test-secret-0123456789abcdef0123456789", publicUrl: ORIGIN,
-  };
+  });
   const ctx: ServerContext = {
     config, db, courses: await createCourseRepository(courseDirs), jobs: fakeJobs,
     auth: { userFromRequest: async () => null },