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/features.ts

@@ -1,8 +1,9 @@
 import type { WebFeature } from "@stc/contracts";
+// Browser-only entries ("@stc/<package>/web", mapped in tsconfig paths and package.json exports). Never import a
+// package's server index here: it pulls Better Auth, git and node:fs into the bundle.
 import { learnerWeb } from "@stc/feature-learner/web";
-import { importWeb } from "../../../packages/feature-import/src/web";
-import { studioWeb } from "../../../packages/feature-studio/src/web";
-import { aiWeb } from "../../../packages/feature-ai/src/web";
+import { importWeb } from "@stc/feature-import/web";
+import { studioWeb } from "@stc/feature-studio/web";
+import { aiWeb } from "@stc/feature-ai/web";
 
-// Phase 1 packages append one import line each and push into this list.
 export const webFeatures: WebFeature[] = [learnerWeb, importWeb, studioWeb, aiWeb];