Add JPA entities

src/main/java/com/seanstarkey/notesvault/entity/Note.java

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+/**
+ * Note.java
+ *
+ * JPA entity representing a user-authored note.
+ */
+package com.seanstarkey.notesvault.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+import org.hibernate.annotations.UuidGenerator;
+import org.springframework.data.annotation.CreatedDate;
+import org.springframework.data.annotation.LastModifiedDate;
+import org.springframework.data.jpa.domain.support.AuditingEntityListener;
+
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+
+@Entity
+@Table(name = "notes")
+@EntityListeners(AuditingEntityListener.class)
+@Getter
+@Setter
+@NoArgsConstructor
+public class Note {
+
+    @Id
+    @UuidGenerator
+    @Column(updatable = false, nullable = false)
+    private UUID id;
+
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
+    @JoinColumn(name = "owner_id", nullable = false)
+    private User owner;
+
+    @Column(nullable = false, length = 255)
+    private String title;
+
+    @Column(nullable = false, columnDefinition = "TEXT")
+    private String content;
+
+    /** Timestamp set once when the record is first persisted. */
+    @CreatedDate
+    @Column(nullable = false, updatable = false)
+    private Instant createdAt;
+
+    @LastModifiedDate
+    @Column(nullable = false)
+    private Instant updatedAt;
+
+    @OneToMany(mappedBy = "note", cascade = CascadeType.ALL, orphanRemoval = true)
+    private List<NoteShare> shares = new ArrayList<>();
+}

src/main/java/com/seanstarkey/notesvault/entity/NoteShare.java

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+/**
+ * NoteShare.java
+ *
+ * JPA entity representing a read-only share grant between a note and a user.
+ */
+package com.seanstarkey.notesvault.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+import org.hibernate.annotations.UuidGenerator;
+import org.springframework.data.annotation.CreatedDate;
+import org.springframework.data.jpa.domain.support.AuditingEntityListener;
+
+import java.time.Instant;
+import java.util.UUID;
+
+@Entity
+@Table(
+    name = "note_shares",
+    uniqueConstraints = @UniqueConstraint(
+        name = "uq_note_shares_note_user",
+        columnNames = {"note_id", "shared_with_user_id"}
+    )
+)
+@EntityListeners(AuditingEntityListener.class)
+@Getter
+@Setter
+@NoArgsConstructor
+public class NoteShare {
+
+    @Id
+    @UuidGenerator
+    @Column(updatable = false, nullable = false)
+    private UUID id;
+
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
+    @JoinColumn(name = "note_id", nullable = false)
+    private Note note;
+
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
+    @JoinColumn(name = "shared_with_user_id", nullable = false)
+    private User sharedWith;
+
+    @CreatedDate
+    @Column(nullable = false, updatable = false)
+    private Instant createdAt;
+}

src/main/java/com/seanstarkey/notesvault/entity/User.java

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+/**
+ * User.java
+ *
+ * JPA entity representing an application user.
+ */
+package com.seanstarkey.notesvault.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+import org.hibernate.annotations.UuidGenerator;
+import org.springframework.data.annotation.CreatedDate;
+import org.springframework.data.jpa.domain.support.AuditingEntityListener;
+
+import java.time.Instant;
+import java.util.UUID;
+
+@Entity
+@Table(name = "users")
+@EntityListeners(AuditingEntityListener.class)
+@Getter
+@Setter
+@NoArgsConstructor
+public class User {
+
+    @Id
+    @UuidGenerator
+    @Column(updatable = false, nullable = false)
+    private UUID id;
+
+    @Column(nullable = false, unique = true, length = 100)
+    private String username;
+
+    @Column(nullable = false)
+    private String passwordHash;
+
+    @CreatedDate
+    @Column(nullable = false, updatable = false)
+    private Instant createdAt;
+}