Background service registration with remote-control, expanded half-page scrolling, and content safety…

Introduces remote-control service manager subcommands to run the CLI as a persistent background daemon, broadens half-page scrolling support and keybindings, and resolves issues with content filter handling, scratch directory watchers, plugin MCP initialization, schema validation, and conversation resumption.

• Added remote-control start, remote-control status, and remote-control stop subcommands to register the CLI with your operating system's service manager as a background daemon that persists across logouts and reboots, including --name for custom instance labels and --session to scope to the active login session.
• Improved half-page scrolling across all views (altscreen mode, diff viewer, and detail panels where Ctrl+D no longer triggers exit prompts) and added Shift+Up and Shift+Down default keybindings (navigation.half_page_up and navigation.half_page_down).
• Fixed prompts or model responses blocked by content safety filters failing with generic errors or empty turns by surfacing explicit content-filter stop reasons.
• Fixed temporary files in scratch/ directories triggering recursive filesystem watchers and cluttering artifact reviews and checkpoints.
• Fixed MCP servers bundled inside global plugins failing to initialize at CLI startup or failing to update running states when plugins are toggled.
• Fixed schema validation errors for third-party MCP server tools whose input schemas omit additionalProperties.
• Fixed redundant filesystem customization discovery walks running on every message when no slash commands were invoked.
• Fixed spurious ERROR: logging before google.Init log lines appearing in cli.log and background daemon outputs.
• Fixed macOS background service lifecycle issues, legacy script cleanup, and paid Google Cloud project license availability for Remote Control.
• Fixed older conversations failing to load with unknown step type errors upon resumption.