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/master/District.java

@@ -0,0 +1,48 @@
+package com.lincfusion.udyamlinc.master;
+
+import jakarta.persistence.*;
+import lombok.*;
+
+/**
+ * The join key for every external signal. Mandi prices and climate series are
+ * pulled per district, never per enterprise — that is what keeps ingestion to
+ * roughly forty rows a day instead of one call per enterprise.
+ */
+@Entity
+@Table(name = "district", indexes = @Index(name = "ix_district_code", columnList = "code", unique = true))
+@Getter
+@Setter
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class District {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    /** SEHORE, VIDISHA… */
+    @Column(nullable = false, unique = true, length = 32)
+    private String code;
+
+    @Column(nullable = false, length = 64)
+    private String name;
+
+    @Column(length = 64)
+    private String nameHi;
+
+    @Column(nullable = false, length = 64)
+    private String state;
+
+    /** District centroid — used to pick the climate grid cell. */
+    private Double latitude;
+
+    private Double longitude;
+
+    private Boolean active;
+
+    @PrePersist
+    void onCreate() {
+        if (active == null) active = Boolean.TRUE;
+    }
+}