feat(api): create knowledge graph API routes (SSC-11)

Add Express routes for knowledge graph endpoints:
- Concept CRUD: POST/GET/PUT/DELETE /concepts
- Relationship CRUD: POST/PUT/DELETE /relationships
- AI extraction: POST /extract (with rate limiting)
- Semantic search: POST /search (with rate limiting)
- Visualization: GET /graph, /strengths, /stats

Author: Sakeeb91

apps/api/src/routes/knowledgeGraph.routes.ts

@@ -0,0 +1,125 @@
+import { Router, Request, Response, NextFunction } from 'express';
+import { rateLimit } from 'express-rate-limit';
+import { knowledgeGraphController } from '../controllers/knowledgeGraph.controller';
+import { authenticateToken } from '../middleware/auth.middleware';
+
+const router = Router();
+
+// Rate limiting for AI extraction (more restrictive due to API costs)
+const extractionLimiter = rateLimit({
+  windowMs: 15 * 60 * 1000, // 15 minutes
+  max: 10, // 10 extraction requests per window
+  message: { error: 'Too many extraction requests, please try again later' },
+  standardHeaders: true,
+  legacyHeaders: false,
+});
+
+// Rate limiting for semantic search
+const searchLimiter = rateLimit({
+  windowMs: 1 * 60 * 1000, // 1 minute
+  max: 30, // 30 search requests per minute
+  message: { error: 'Too many search requests, please try again later' },
+  standardHeaders: true,
+  legacyHeaders: false,
+});
+
+// All routes require authentication
+router.use(authenticateToken);
+
+// ============================================
+// CONCEPTS
+// ============================================
+
+// POST /api/knowledge-graph/concepts - Create a new concept
+router.post('/concepts', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.createConcept(req, res, next)
+);
+
+// GET /api/knowledge-graph/concepts - Get all concepts for current user
+router.get('/concepts', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.getConcepts(req, res, next)
+);
+
+// GET /api/knowledge-graph/concepts/:id - Get a specific concept
+router.get('/concepts/:id', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.getConcept(req, res, next)
+);
+
+// PUT /api/knowledge-graph/concepts/:id - Update a concept
+router.put('/concepts/:id', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.updateConcept(req, res, next)
+);
+
+// DELETE /api/knowledge-graph/concepts/:id - Delete a concept
+router.delete('/concepts/:id', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.deleteConcept(req, res, next)
+);
+
+// GET /api/knowledge-graph/concepts/:id/similar - Find similar concepts
+router.get('/concepts/:id/similar', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.findSimilar(req, res, next)
+);
+
+// ============================================
+// RELATIONSHIPS
+// ============================================
+
+// POST /api/knowledge-graph/relationships - Create a relationship
+router.post('/relationships', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.createRelationship(req, res, next)
+);
+
+// PUT /api/knowledge-graph/relationships/:id - Update a relationship
+router.put('/relationships/:id', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.updateRelationship(req, res, next)
+);
+
+// DELETE /api/knowledge-graph/relationships/:id - Delete a relationship
+router.delete('/relationships/:id', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.deleteRelationship(req, res, next)
+);
+
+// ============================================
+// AI EXTRACTION
+// ============================================
+
+// POST /api/knowledge-graph/extract - Extract concepts from an upload
+router.post(
+  '/extract',
+  extractionLimiter,
+  (req: Request, res: Response, next: NextFunction) =>
+    knowledgeGraphController.extractFromUpload(req, res, next)
+);
+
+// ============================================
+// SEMANTIC SEARCH
+// ============================================
+
+// POST /api/knowledge-graph/search - Semantic search across concepts
+router.post(
+  '/search',
+  searchLimiter,
+  (req: Request, res: Response, next: NextFunction) =>
+    knowledgeGraphController.semanticSearch(req, res, next)
+);
+
+// ============================================
+// VISUALIZATION & STATISTICS
+// ============================================
+
+// GET /api/knowledge-graph/graph - Get graph data for visualization
+router.get('/graph', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.getGraph(req, res, next)
+);
+
+// GET /api/knowledge-graph/strengths - Get concept strength scores
+router.get('/strengths', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.getConceptStrengths(req, res, next)
+);
+
+// GET /api/knowledge-graph/stats - Get knowledge graph statistics
+router.get('/stats', (req: Request, res: Response, next: NextFunction) =>
+  knowledgeGraphController.getStats(req, res, next)
+);
+
+export default router;