feat: implement AI tutor memory and RAG system for continuous learning

- Added chat sessions and message persistence for interaction history.
- Integrated Knowledge Base (RAG) using PostgreSQL Full Text Search.
- Implemented automated ingestion of lesson content during course sync.
- Updated AITutor frontend to support persistent session IDs via localStorage.
- Added database migrations for chat_sessions, chat_messages, and knowledge_base.
- Fixed SQLx build issues to allow offline Docker image compilation.

services/lms-service/migrations/20260123000001_ai_training.sql

@@ -0,0 +1,39 @@
+-- Migration: AI Training (Memory & RAG)
+-- Create tables for chat persistent memory and knowledge base ingestion
+
+-- 1. Chat Sessions Table
+CREATE TABLE IF NOT EXISTS chat_sessions (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    organization_id UUID NOT NULL REFERENCES organizations(id) ON DELETE CASCADE,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    lesson_id UUID REFERENCES lessons(id) ON DELETE CASCADE,
+    title TEXT,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- 2. Chat Messages Table
+CREATE TABLE IF NOT EXISTS chat_messages (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    session_id UUID NOT NULL REFERENCES chat_sessions(id) ON DELETE CASCADE,
+    role VARCHAR(20) NOT NULL, -- 'user' or 'assistant'
+    content TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_chat_messages_session_id ON chat_messages(session_id);
+
+-- 3. Knowledge Base Table
+CREATE TABLE IF NOT EXISTS knowledge_base (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    organization_id UUID NOT NULL REFERENCES organizations(id) ON DELETE CASCADE,
+    source_type VARCHAR(50) NOT NULL, -- 'lesson_content', 'file_supplementary', 'interaction_summary'
+    source_id UUID, -- References lesson_id, file_id, etc.
+    content_chunk TEXT NOT NULL,
+    search_vector tsvector GENERATED ALWAYS AS (to_tsvector('english', content_chunk)) STORED,
+    metadata JSONB, -- Additional info like chapter, page number, etc.
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Index for Full Text Search
+CREATE INDEX IF NOT EXISTS idx_knowledge_base_search ON knowledge_base USING GIN(search_vector);
+CREATE INDEX IF NOT EXISTS idx_knowledge_base_org_on ON knowledge_base(organization_id);