Split into per-article modules and add the method-security module

Moves the existing virtual-thread/context-propagation project into
context-propagation/ and adds method-security/ for the Spring Security 7
method-security article: nine runnable demos, fourteen assertions, and every
transcript the article quotes, regenerated by scripts/run-all.sh.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RSrsDSRKVsY588yFiMJMo9

method-security/src/main/java/com/ankurm/methodsec/Account.java

@@ -0,0 +1,51 @@
+package com.ankurm.methodsec;
+
+/**
+ * The one domain object every demo in this module operates on.
+ *
+ * <p>{@code owner} is deliberately a plain {@code String} that matches
+ * {@code authentication.getName()}, because that is what makes expressions like
+ * {@code returnObject.owner == authentication.name} readable in the SpEL reference
+ * (<a href="../../../../../../docs/02-spel-reference.md">docs/02-spel-reference.md</a>).
+ *
+ * <p>Not a record: {@link Demo7DeniedHandling} needs a CGLIB-proxyable, non-final class for
+ * {@code @AuthorizeReturnObject}, and records are final. That restriction is itself one of the
+ * findings -- see
+ * <a href="../../../../../../docs/06-denied-handling.md">docs/06-denied-handling.md</a>.
+ */
+public class Account {
+
+	private final long id;
+
+	private final String owner;
+
+	private long balanceMinor;
+
+	public Account(long id, String owner, long balanceMinor) {
+		this.id = id;
+		this.owner = owner;
+		this.balanceMinor = balanceMinor;
+	}
+
+	public long getId() {
+		return this.id;
+	}
+
+	public String getOwner() {
+		return this.owner;
+	}
+
+	public long getBalanceMinor() {
+		return this.balanceMinor;
+	}
+
+	public void setBalanceMinor(long balanceMinor) {
+		this.balanceMinor = balanceMinor;
+	}
+
+	@Override
+	public String toString() {
+		return "Account[" + this.id + "," + this.owner + "," + this.balanceMinor + "]";
+	}
+
+}