feat(learner): web shell, library, lesson views (LessonView), decks, code files, exercises, notes, account and admin pages

Tasks 10-12 of the WP-A plan in one commit (the route modules import each other):
- header extras portalled into the Phase 0 header: course switcher, search, Reading/Work, account
- course frame with outline sidebar (mobile overlay, Escape closes), progress, gating locks
- library: featured course, continue row, New and collection rows, course list, filters, search
- LessonView: text (track switcher, folds, ordered hint tiers), video (resume, done near the end,
  timestamp notes, transcript), companion decks rendered with pdf.js (thumbs, arrows, fullscreen,
  per-slide notes), code files (tree, tabs, copy, zip, command), exercises (Web Worker runner or
  local command with optional pasted evidence), floating action bar
- notes list, account (email/password, providers, SSO by email) and owner admin pages
- pdf.js worker served from /api/learner/pdf.worker.mjs
- browser entry @stc/feature-learner/web (the package index also carries the server half)

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

packages/feature-learner/test/assets.test.ts

@@ -0,0 +1,11 @@
+import { expect } from "bun:test";
+import { forEachDb } from "./helpers";
+import { makeApp } from "./app";
+
+forEachDb("the pdf.js worker is served for client-side deck rendering", async (db) => {
+  const { call } = await makeApp(db);
+  const r = await call("GET", "/api/learner/pdf.worker.mjs");
+  expect(r.status).toBe(200);
+  expect(r.headers.get("content-type")).toContain("javascript");
+  expect((await r.text()).length).toBeGreaterThan(100_000);
+});