feat: add persistent CLI config defaults

[elliotllliu]

Summary

Closes #678 — adds a skills config command to persist CLI flags across invocations.

Problem

Users who frequently use flags like -y, -g, --agent, --copy, and --json have to re-enter them for every command, which is tedious and error-prone.

Solution

A simple config system stored in ~/.skills/config.json:

# Set defaults
skills config set global true         # always install globally
skills config set yes true            # skip prompts by default
skills config set agent claude-code   # default agent
skills config set json true           # default JSON output
skills config set copy true           # copy instead of symlink

# Manage config
skills config list                    # show current defaults
skills config unset global            # remove a default
skills config path                    # show config file location

Config defaults are automatically merged into add, remove, list, check, and sync commands. Explicit CLI flags always take precedence over config defaults.

Changes

• src/config.ts: New module — loadConfig(), saveConfig(), runConfig() with validation for known keys
• src/cli.ts: Import config, add config command, merge defaults into each command's options before execution

Design Decisions

• Config file at ~/.skills/config.json — simple, human-readable, easy to edit manually
• Only boolean/string-array keys supported (global, yes, copy, json, agent)
• CLI flags always override config — no surprises
• No new dependencies

[DaVinci42]

Thanks!

Current impl stores config in ~/.skills/config.json which works, but a more idiomatic approach per platform would be:

• macOS/Linux: Follow the XDG base directory spec use, $XDG_CONFIG_HOME/skills/config.json , falling back to ~/.config/skills/config.json. This keeps $HOME clean.

• Windows: The conventional location is %APPDATA%\skills\config.json (i.e. C:\Users<user>\AppData\Roaming\skills\config.json ), which is where user-scoped app config lives by OS convention.

Some libraries like env-paths handles all three platforms automatically and is already popular in the node ecosystem, might be worth the one-liner dependency to get this right without reinventing it.

The skills install paths themselves are already a bit of a wild west ( ~/.skills/ , ~/.agents/ , per-agent dirs, etc.). But the CLI binary's own config is a clean slate, and it's worth getting the convention right from the start.

[elliotllliu]

Good point! Updated in 504a0e3 to use platform-idiomatic paths:

• Linux: $XDG_CONFIG_HOME/skills/config.json (fallback ~/.config/skills/config.json)
• macOS: ~/Library/Application Support/skills/config.json
• Windows: %APPDATA%\skills\config.json

Kept it dependency-free using process.platform detection — no need for env-paths since the logic is straightforward for three platforms.

Thanks for the suggestion!