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/git-branch.test.ts

@@ -5,7 +5,7 @@ import * as fs from "node:fs";
 import { GitBranch } from "../core/git-branch.js";
 
 function createTempRepo(): string {
-  const dir = fs.mkdtempSync(path.join(os.tmpdir(), "ci-branch-test-"));
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), "ciagent-branch-test-"));
   execSync("git init", { cwd: dir, stdio: "pipe" });
   execSync('git config user.email "test@test.com"', { cwd: dir, stdio: "pipe" });
   execSync('git config user.name "Test"', { cwd: dir, stdio: "pipe" });