Add stats and achievements CRUD commands

[cloud9c]

Summary

• Adds wvdsh stats subcommands: list, create, update, delete for managing game stats
• Adds wvdsh achievements subcommands: list, create, update, delete for managing game achievements
• Extracts shared HTTP client logic into a reusable ApiClient struct (api_client.rs)

Usage

wvdsh stats list
wvdsh stats create kills_total --display-name "Total Kills" --authority client --type integer
wvdsh stats update kills_total --display-name "Lifetime Kills"
wvdsh stats delete kills_total

wvdsh achievements list
wvdsh achievements create first_blood --display-name "First Blood" --description "Get your first kill" --image "img.png" --authority client --points 10
wvdsh achievements update first_blood --points 25 --stat-identifier kills_total --stat-threshold 1
wvdsh achievements update first_blood --stat-identifier none  # unlink stat
wvdsh achievements delete first_blood

Test plan

• cargo check passes
• cargo clippy — no new warnings
• Manual test against staging: stats list/create/update/delete cycle
• Manual test against staging: achievements list/create/update/delete cycle

🤖 Generated with Claude Code