chore: initial commit — UdyamLinc backend, phases A-E

Spring Boot 4 / Java 17 / Postgres. Masters and serving (A), Agmarknet and
climate ingestion (B), feature store with 14 derivations (C), SpEL rule
engine and risk scoring (D).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/main/java/com/lincfusion/udyamlinc/common/GlobalExceptionHandler.java

@@ -0,0 +1,44 @@
+package com.lincfusion.udyamlinc.common;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+import java.util.stream.Collectors;
+
+/** Every failure leaves the service in the same envelope the UI already parses. */
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(ResourceNotFoundException.class)
+    public ResponseEntity<ApiResponse<Void>> notFound(ResourceNotFoundException e) {
+        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ApiResponse.fail(e.getMessage()));
+    }
+
+    @ExceptionHandler(BadCredentialsException.class)
+    public ResponseEntity<ApiResponse<Void>> badCredentials(BadCredentialsException e) {
+        return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body(ApiResponse.fail(e.getMessage()));
+    }
+
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    public ResponseEntity<ApiResponse<Void>> invalid(MethodArgumentNotValidException e) {
+        String detail = e.getBindingResult().getFieldErrors().stream()
+                .map(f -> f.getField() + " " + f.getDefaultMessage())
+                .collect(Collectors.joining("; "));
+        return ResponseEntity.badRequest().body(ApiResponse.fail(detail));
+    }
+
+    @ExceptionHandler(IllegalArgumentException.class)
+    public ResponseEntity<ApiResponse<Void>> illegal(IllegalArgumentException e) {
+        return ResponseEntity.badRequest().body(ApiResponse.fail(e.getMessage()));
+    }
+
+    @ExceptionHandler(Exception.class)
+    public ResponseEntity<ApiResponse<Void>> unexpected(Exception e) {
+        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+                .body(ApiResponse.fail("Unexpected error: " + e.getMessage()));
+    }
+}