feat: add collaborative document functionality for lessons

- Create migration scripts for lesson_collaborative_docs table in both cms-service and lms-service.
- Implement CollaborativeDocEditor component for real-time editing of collaborative documents.
- Add LessonCollaborativeDocPage for instructors to view and manage collaborative documents.
- Include conflict resolution handling in the editor.
- Enhance UI with status indicators and formatting options for the document editor.

Co-authored-by: Copilot <copilot@github.com>

services/cms-service/migrations/20260427000007_collaborative_docs.sql

@@ -0,0 +1,15 @@
+-- Fase 40: Documentos Colaborativos (cms-service mirror)
+CREATE TABLE IF NOT EXISTS lesson_collaborative_docs (
+    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    lesson_id       UUID NOT NULL,
+    organization_id UUID NOT NULL,
+    course_id       UUID NOT NULL,
+    content         TEXT NOT NULL DEFAULT '',
+    revision        BIGINT NOT NULL DEFAULT 0,
+    last_modified_by UUID,
+    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_collab_docs_lesson
+    ON lesson_collaborative_docs (lesson_id, organization_id);