New --project-config-root flag lets a host override the project directory everywhere

What

• A new --project-config-root CLI flag lets a host pin the "project" directory used for CLAUDE.md discovery, project settings, skills directories, .mcp.json resolution, scheduled tasks, and plugin environment variables like CLAUDE_PROJECT_DIR, instead of always deriving it from the current working directory.
• Internally, a new accessor (host.launchOptions.projectConfigRoot()) is now checked ahead of the normal working-directory-based project root in many places: project settings path resolution, CLAUDE_SKILL_DIR/CLAUDE_PROJECT_DIR substitution in skills and slash commands, the environment and working directory used to spawn MCP stdio servers, and the working directory used for LSP server processes. When this override is set, dynamic skill-directory scanning is skipped entirely.
• Hook execution and path handling, and subagent statusLine scripts, now also resolve their working directory and CLAUDE_PROJECT_DIR from this override before falling back to the normal project root.

Why

This lets a host application run Claude Code against a project directory that differs from the process's actual working directory, useful when embedding Claude Code somewhere the "project" isn't simply wherever the process happened to start.