feat(claude): support Claude Desktop import pointers and Claude Cloud migration

[elijahr]

Summary

Adds support for Claude Desktop session discovery on import and migrating from Claude Cloud exports.

• Claude Desktop companion pointer: When importing or converting to Claude format (--to claude), writes the native Claude Code JSONL session to ~/.claude/projects/ and generates the companion local_<cliSessionId>.json pointer under claude-code-sessions/<org_id>/<project_id>/ so imported sessions appear simultaneously in both Claude Desktop and Claude Code CLI.
• Cross-platform Desktop detection: Automatically resolves standard claude-code-sessions directories on macOS (~/Library/Application Support/Claude), Linux (~/.config/Claude), and Windows (%APPDATA%/Claude), with support for --claude-desktop-dir and CLAUDE_DESKTOP_CONFIG_DIR.
• Project directory matching: Dynamically maps to an existing project by matching session cwd, falls back to the active org/project directory, or initializes the default 00000000-0000-4000-8000-000000000001 pair.
• Claude Cloud migration: Adds AgentFormat.CLAUDE_CLOUD = "claude-cloud" read-only source adapter to ingest Claude.ai data export bundles (conversations.json or individual conversation JSON files).
• Format detection & conversion: Supports auto-detection and --from claude-cloud across inspect, convert, import, and catalog discovery.

Validation

• Clean linting: uv run ruff check . passed with 0 errors.
• Test suite: uv run pytest -q passed 1,543 tests, 55 skipped (100% pass rate).
• Unit tests added: 24 new tests in tests/test_claude_desktop.py and tests/test_claude_cloud.py covering desktop pointer generation, path resolution, collision handling, and cloud format ingestion.