fix: honor CLAUDE_CONFIG_DIR environment variable (#261)

Fixes #255

- Add getClaudeConfigDir() utility function that respects CLAUDE_CONFIG_DIR env var
- Update all hardcoded ~/.claude paths to use the new utility
- Add comprehensive tests for getClaudeConfigDir()
- Maintain backward compatibility with default ~/.claude when env var is not set

Files updated:
- src/shared/claude-config-dir.ts (new utility)
- src/shared/claude-config-dir.test.ts (tests)
- src/hooks/claude-code-hooks/config.ts
- src/hooks/claude-code-hooks/todo.ts
- src/hooks/claude-code-hooks/transcript.ts
- src/features/claude-code-command-loader/loader.ts
- src/features/claude-code-agent-loader/loader.ts
- src/features/claude-code-skill-loader/loader.ts
- src/features/claude-code-mcp-loader/loader.ts
- src/tools/session-manager/constants.ts
- src/tools/slashcommand/tools.ts

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/hooks/claude-code-hooks/transcript.ts

@@ -1,15 +1,12 @@
-/**
- * Transcript Manager
- * Creates and manages Claude Code compatible transcript files
- */
 import { join } from "path"
 import { mkdirSync, appendFileSync, existsSync, writeFileSync, unlinkSync } from "fs"
-import { homedir, tmpdir } from "os"
+import { tmpdir } from "os"
 import { randomUUID } from "crypto"
 import type { TranscriptEntry } from "./types"
 import { transformToolName } from "../../shared/tool-name"
+import { getClaudeConfigDir } from "../../shared"
 
-const TRANSCRIPT_DIR = join(homedir(), ".claude", "transcripts")
+const TRANSCRIPT_DIR = join(getClaudeConfigDir(), "transcripts")
 
 export function getTranscriptPath(sessionId: string): string {
   return join(TRANSCRIPT_DIR, `${sessionId}.jsonl`)