feat(project): add --label flag to project create and update

[KinomotoMio]

Summary

• Adds repeatable --label <label> to linear project create and linear project update for Linear ProjectLabel IDs.
• Resolves project labels case-insensitively and creates missing labels via projectLabelCreate without forcing a color.
• Keeps project update --label additive by preserving current project label IDs and appending new ones.
• Adds interactive project label selection for project create -i, including a create-new option.

Test plan

• npx --yes deno@2.7.9 task codegen
• npx --yes deno@2.7.9 task check
• npx --yes deno@2.7.9 lint
• TZ=UTC npx --yes deno@2.7.9 task test (337 passed, 5 ignored)
• TZ=UTC npx --yes deno@2.7.9 test --allow-all --quiet test/commands/project/project-create.test.ts test/commands/project/project-update.test.ts