refactor(rebrand): rename & rebrand CI → CIAgent across all source and test files

- Type renames: CIConfig → CIAgentConfig, DEFAULT_CI_CONFIG → DEFAULT_CIAGENT_CONFIG
- Type renames: CiMetadata → CIAgentMetadata, ParsedCiCommit → ParsedCIAgentCommit
- Function renames: initCI → initCIAgent, isCIInitialized → isCIAgentInitialized
- Function renames: extractCiBlock → extractCIAgentBlock, parseCiBlock → parseCIAgentBlock
- Class renames: CiFiles → CIAgentFiles
- Import paths: ci-files.js → ciagent-files.js
- Directory paths: .ci/ → .ciagent/ across all source and test files
- Check names: ".ci directory exists" → ".ciagent directory exists"
- Check names: "CI config valid" → "CIAgent config valid"
- Temp dir names: ci-*-test- → ciagent-*-test-
- CLI examples: "ci init" → "ciagent init"
- Fix deepMerge infinite recursion bug in config.ts
- ---ci---/---/ci--- block markers preserved unchanged
- All 31 test suites, 370 tests passing

---ci---
phase: 1
milestone: v0.5
plan: 07
task: 07-01-01
status: execute
---/ci---

src/core/artifacts.test.ts

@@ -8,7 +8,7 @@ describe("ArtifactManager", () => {
   let manager: ArtifactManager;
 
   beforeEach(() => {
-    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "ci-artifact-test-"));
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "ciagent-artifact-test-"));
     manager = new ArtifactManager(tempDir);
   });
 
@@ -17,16 +17,16 @@ describe("ArtifactManager", () => {
   });
 
   describe("ensureStructure", () => {
-    it("creates .ci directory structure", () => {
+    it("creates .ciagent directory structure", () => {
       manager.ensureStructure();
-      expect(fs.existsSync(path.join(tempDir, ".ci"))).toBe(true);
-      expect(fs.existsSync(path.join(tempDir, ".ci", "audit"))).toBe(true);
+      expect(fs.existsSync(path.join(tempDir, ".ciagent"))).toBe(true);
+      expect(fs.existsSync(path.join(tempDir, ".ciagent", "audit"))).toBe(true);
     });
 
     it("is idempotent", () => {
       manager.ensureStructure();
       manager.ensureStructure();
-      expect(fs.existsSync(path.join(tempDir, ".ci"))).toBe(true);
+      expect(fs.existsSync(path.join(tempDir, ".ciagent"))).toBe(true);
     });
   });
 
@@ -67,7 +67,7 @@ describe("ArtifactManager", () => {
 
       manager.writeProject(manifest);
 
-      const projectPath = path.join(tempDir, ".ci", "PROJECT.md");
+      const projectPath = path.join(tempDir, ".ciagent", "PROJECT.md");
       expect(fs.existsSync(projectPath)).toBe(true);
       const content = fs.readFileSync(projectPath, "utf-8");
       expect(content).toContain("Test Project");
@@ -131,7 +131,7 @@ describe("ArtifactManager", () => {
         ],
       });
 
-      const decisionsPath = path.join(tempDir, ".ci", "DECISIONS.md");
+      const decisionsPath = path.join(tempDir, ".ciagent", "DECISIONS.md");
       expect(fs.existsSync(decisionsPath)).toBe(true);
       const content = fs.readFileSync(decisionsPath, "utf-8");
       expect(content).toContain("D-001");