feat: HLS streaming, transcripts, agent course generation & landing-page course previews (#663)

New features:
- HLS video encoding/streaming (hls routes, hls-encoder) and a media
  transcripts pipeline (transcripts route + media-transcript queries)
- AI assistant chat vs. run model: agent-course-generation worker/queue,
  run-monitor pane, chat-changes card, content ask-ai bar
- Per-theme course-page previews across org landing-page themes (bold,
  classic, corporate, editorial, etc.) with a shared course token/component set
- View-as-student mode and login-link / link-invite invite flows

Refactor:
- Extract packages/core consolidating config (env, storage, dashboard-url),
  services and utils previously duplicated under apps/api/src/config
- Remove legacy agent service modules (chat-tools, chat-context,
  context-window, document, fetch-url, lesson-content)
- Relax Cross-Origin-Resource-Policy to allow cross-origin media embedding
- Add format script to tenant-router so turbo run format covers it

packages/ui/src/custom/org-landing-page/course-section-nav.svelte

@@ -0,0 +1,71 @@
+<script lang="ts">
+  import type { CourseLandingPageLabels, OrgLandingPageTheme } from './types';
+  import { courseLandingTokens } from './course-landing-page.tokens';
+  import * as UnderlineTabs from '../underline-tabs';
+
+  interface SectionNavItem {
+    /** DOM id of the section to scroll to (without leading #). */
+    id: string;
+    label: string;
+  }
+
+  interface Props {
+    variant: OrgLandingPageTheme;
+    items: SectionNavItem[];
+    labels?: CourseLandingPageLabels;
+  }
+
+  let { variant, items }: Props = $props();
+
+  const t = $derived(courseLandingTokens(variant));
+
+  let activeId = $state<string>('');
+
+  $effect(() => {
+    if (typeof window === 'undefined') return;
+    if (items.length === 0) return;
+
+    const elements = items.map(({ id }) => document.getElementById(id)).filter((el): el is HTMLElement => el !== null);
+
+    if (elements.length === 0) return;
+
+    const observer = new IntersectionObserver(
+      (entries) => {
+        const visible = entries
+          .filter((e) => e.isIntersecting)
+          .sort((a, b) => b.intersectionRatio - a.intersectionRatio);
+        if (visible[0]) activeId = visible[0].target.id;
+      },
+      {
+        rootMargin: '-120px 0px -55% 0px',
+        threshold: [0, 0.25, 0.5, 0.75, 1]
+      }
+    );
+
+    elements.forEach((el) => observer.observe(el));
+    return () => observer.disconnect();
+  });
+
+  function handleScroll(id: string) {
+    const el = document.getElementById(id);
+    if (!el) return;
+    const top = el.getBoundingClientRect().top + window.scrollY - 24;
+    window.scrollTo({ top, behavior: 'smooth' });
+  }
+</script>
+
+{#if items.length > 1}
+  <nav class={t.sectionNavShell}>
+    <div class={t.sectionNavInner}>
+      <UnderlineTabs.Root bind:value={activeId} class="ui:w-full">
+        <UnderlineTabs.List class={t.sectionNavList}>
+          {#each items as item (item.id)}
+            <UnderlineTabs.Trigger value={item.id} class={t.sectionNavItem} onclick={() => handleScroll(item.id)}>
+              {item.label}
+            </UnderlineTabs.Trigger>
+          {/each}
+        </UnderlineTabs.List>
+      </UnderlineTabs.Root>
+    </div>
+  </nav>
+{/if}