artcraft-mcp: fold crate into the parent workspace

Drop the standalone [workspace] block from the crate's Cargo.toml and
add 'crates/cli/artcraft-mcp' to the root workspace members list.

Kept this as the final commit on the branch — until this lands the
crate was a separate workspace, which kept the root Cargo.toml
untouched during the spike (avoiding conflicts with parallel work on
main) but meant 'cargo build' at the repo root didn't include it.

After this commit, 'cargo check -p artcraft-mcp' works from the repo
root and the crate is a first-class workspace member.

Cargo.toml

@@ -30,6 +30,7 @@ members = [
   "crates/api_clients/worldlabs_consumer_client",
 
   # CLI tools for operations, etc.
+  "crates/cli/artcraft-mcp",
   "crates/cli/devenv/dev-database-seed",
   "crates/cli/devenv/dev-upload-media-file",
   "crates/cli/production/db-backfill",

crates/cli/artcraft-mcp/Cargo.toml

@@ -1,9 +1,3 @@
-[workspace]
-# Standalone workspace during the MVP spike — keeps us out of the root
-# workspace's Cargo.toml until the final commit so other agents on `main`
-# don't collide with this work. Will be merged into the parent workspace
-# as the last step (see docs/mcp-integration-plan.md, Phase 6).
-
 [package]
 name = "artcraft-mcp"
 version = "0.0.1"