feat: claudely setup — interactive configuration wizard #14

Summary

Add a claudely setup subcommand that walks the user through configuring their provider, base URL, auth token, and default model via an interactive wizard. Values persist to a platform-native config file and load on every subsequent claudely invocation.

Design spec

See docs/superpowers/specs/2026-05-03-setup-wizard-design.md for the full design.

Key decisions

• Config location: XDG on Linux (~/.config/claudely/config.json), ~/Library/Application Support/ on macOS, %APPDATA% on Windows
• Precedence: CLI flag > env var > config file > provider default
• loadSettings decoupling: moves from compat.ts to new config.ts — all config I/O in one module, compat.ts keeps only business logic
• Re-run behavior: shows current saved values as editable defaults (no "overwrite?" prompt)

New files

• src/config.ts — configDir(), configPath(), loadConfig(), saveConfig(), loadSettings() (moved from compat.ts)
• src/setup.ts — runSetup() (interactive wizard flow)
• src/config.test.ts — unit tests for config persistence

Changes to existing files

• src/compat.ts — remove loadSettings() and fs import (pure business logic only)
• src/cli.ts — subcommand dispatch for setup, import loadSettings from config.ts, thread config into resolution chain

Wizard flow

1. Pick provider (select from registry)
2. Base URL (pre-filled with provider default or saved value)
3. Auth token (pre-filled)
4. Test connection (/v1/models with 5s timeout, non-blocking)
5. Pick default model (from discovered models, or manual entry)
6. Confirm & save

Acceptance

• claudely setup walks through all 6 wizard steps
• Config persists to platform-native path
• Saved config loads on subsequent claudely runs
• Precedence: CLI flag > env var > config > provider default
• Re-running setup pre-fills with saved values
• loadSettings moved from compat.ts to config.ts
• src/config.test.ts covers round-trip, missing file, corrupt JSON, directory creation
• Existing tests still pass