fix: revert unauthorized $CMEM branding in context header

A prior Claude instance snuck in a `$CMEM` token branding header
during a context compression refactor (7e072106). Reverts back to
the original descriptive format: `# [project] recent context, datetime`

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/context/formatters/AgentFormatter.ts

@@ -35,7 +35,7 @@ function formatHeaderDateTime(): string {
  */
 export function renderAgentHeader(project: string): string[] {
   return [
-    `# $CMEM ${project} ${formatHeaderDateTime()}`,
+    `# [${project}] recent context, ${formatHeaderDateTime()}`,
     ''
   ];
 }
@@ -223,5 +223,5 @@ export function renderAgentFooter(totalDiscoveryTokens: number, totalReadTokens:
  * Render agent empty state
  */
 export function renderAgentEmptyState(project: string): string {
-  return `# $CMEM ${project} ${formatHeaderDateTime()}\n\nNo previous sessions found.`;
+  return `# [${project}] recent context, ${formatHeaderDateTime()}\n\nNo previous sessions found.`;
 }

tests/context/formatters/agent-formatter.test.ts

@@ -103,7 +103,7 @@ describe('AgentFormatter', () => {
       const result = renderAgentHeader('my-project');
 
       expect(result).toHaveLength(2);
-      expect(result[0]).toMatch(/^# \$CMEM my-project \d{4}-\d{2}-\d{2} \d{1,2}:\d{2}[ap]m [A-Z]{3,4}$/);
+      expect(result[0]).toMatch(/^# \[my-project\] recent context, \d{4}-\d{2}-\d{2} \d{1,2}:\d{2}[ap]m [A-Z]{3,4}$/);
       expect(result[1]).toBe('');
     });
 
@@ -116,7 +116,7 @@ describe('AgentFormatter', () => {
     it('should handle empty project name', () => {
       const result = renderAgentHeader('');
 
-      expect(result[0]).toMatch(/^# \$CMEM  \d{4}-\d{2}-\d{2} \d{1,2}:\d{2}[ap]m [A-Z]{3,4}$/);
+      expect(result[0]).toMatch(/^# \[\] recent context, \d{4}-\d{2}-\d{2} \d{1,2}:\d{2}[ap]m [A-Z]{3,4}$/);
     });
   });
 
@@ -452,7 +452,7 @@ describe('AgentFormatter', () => {
     it('should return helpful message with project name', () => {
       const result = renderAgentEmptyState('my-project');
 
-      expect(result).toContain('# $CMEM my-project');
+      expect(result).toContain('# [my-project] recent context,');
       expect(result).toContain('No previous sessions found.');
     });
 
@@ -466,7 +466,7 @@ describe('AgentFormatter', () => {
     it('should handle empty project name', () => {
       const result = renderAgentEmptyState('');
 
-      expect(result).toContain('# $CMEM ');
+      expect(result).toContain('# [] recent context,');
     });
   });
 });