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/web/src/nav.test.ts

@@ -0,0 +1,21 @@
+import { expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+import { webFeatures } from "./features";
+import { visibleNav } from "./nav";
+
+const labels = (roles: ("owner" | "author" | "learner")[] | null) => visibleNav(webFeatures, roles ? { roles } : null).map((r) => r.nav!.label);
+
+test("nav items are limited by role", () => {
+  expect(labels(null)).toEqual([]);
+  expect(labels(["learner"])).toEqual([]);
+  expect(labels(["author"])).toEqual(["Studio"]);
+  expect(labels(["owner"])).toEqual(["Studio", "Import", "AI"]);
+});
+
+test("features.ts imports only browser entries, by package name", () => {
+  const src = readFileSync(join(import.meta.dir, "features.ts"), "utf8");
+  const specs = [...src.matchAll(/from\s+"([^"]+)"/g)].map((m) => m[1]!);
+  for (const s of specs) expect(s === "@stc/contracts" || /^@stc\/feature-[a-z]+\/web$/.test(s)).toBe(true);
+  expect(specs.filter((s) => s.endsWith("/web")).length).toBe(4);
+});