Improve issue create project selection

[mbuvarp]

Summary

This improves linear issue create in three related areas:

• allow --project to keep issue creation interactive, the same way --parent already does
• add optional project selection in interactive issue creation
• add configurable default self-assignment behavior for created issues

Before this change, linear issue create --project "Dashboard" skipped interactive mode and failed with "Title is required when not using interactive mode". With this PR, --project is treated as an interactive-safe input, so users can preselect a project without also needing --title.

Project prompting in interactive mode remains opt-in. issue_create_ask_project defaults to false, so existing interactive behavior is unchanged unless users explicitly enable the new prompt.

Changes

• allow interactive issue creation when the only flags are --project, --parent, or both
• add a team-scoped project picker during interactive issue creation
• gate the direct project prompt behind a new config option: issue_create_ask_project
• keep issue_create_ask_project = false as the default, so project selection stays out of the main interactive flow unless enabled
• when issue_create_ask_project = false, expose Project through the existing "Add more fields" flow instead
• continue inheriting the parent issue's project when --parent is used without an explicit --project
• allow explicit --project together with --parent and defer any invalid combination checks to the Linear API
• add a new config option, issue_create_assign_self, with these modes:
  • auto (default): respect Linear's autoAssignToSelf setting
  • always: default-assign created issues to self
  • never: never default-assign created issues
• update docs for the new interactive behavior and config options

Notes

• issue_create_ask_project defaults to false, so users who do not set it will keep the previous interactive flow
• project selection only shows projects available to the selected team
• the interactive project picker is not shown when a parent issue is present unless the project was explicitly provided
• explicit --assignee, the interactive assignee flow, and --start still override the default assignment behavior

Testing

• deno task codegen
• deno task check
• deno lint
• deno fmt
• deno task generate-skill-docs
• deno test --allow-all --quiet test/config.test.ts
• deno test --allow-all --quiet test/commands/issue/issue-create.test.ts