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/tools/session-manager/constants.ts

@@ -1,12 +1,12 @@
 import { join } from "node:path"
-import { homedir } from "node:os"
 import { getOpenCodeStorageDir } from "../../shared/data-path"
+import { getClaudeConfigDir } from "../../shared"
 
 export const OPENCODE_STORAGE = getOpenCodeStorageDir()
 export const MESSAGE_STORAGE = join(OPENCODE_STORAGE, "message")
 export const PART_STORAGE = join(OPENCODE_STORAGE, "part")
-export const TODO_DIR = join(homedir(), ".claude", "todos")
-export const TRANSCRIPT_DIR = join(homedir(), ".claude", "transcripts")
+export const TODO_DIR = join(getClaudeConfigDir(), "todos")
+export const TRANSCRIPT_DIR = join(getClaudeConfigDir(), "transcripts")
 export const SESSION_LIST_DESCRIPTION = `List all OpenCode sessions with optional filtering.
 
 Returns a list of available session IDs with metadata including message count, date range, and agents used.