feat(examples): add automated setup scripts for statusline and title

[weby-homelab]

This PR introduces automated setup.sh scripts for both the custom statusline and the custom terminal title examples.

Problem

Previously, configuring the custom statusline or window title was a manual multi-step process that required:

1. Copying the script from the cloned repository to a global settings directory (so it stays configured even if the repo is deleted/moved).
2. Figuring out the platform-specific config directory (Linux vs macOS vs Windows).
3. Editing settings.json manually to set the exact absolute path to the script and enabling the feature.
4. Additionally, some documentation referred to non-existent slash commands like /statusline enable.

Solution

This PR adds two simple scripts:

• examples/statusline/setup.sh
• examples/title/setup.sh

Running either script will automatically:

1. Detect the platform's settings directory (~/.gemini/antigravity-cli on Linux, ~/Library/Application Support/antigravity-cli on macOS, and %APPDATA%\\antigravity-cli on Windows).
2. Copy the corresponding helper script (statusline.sh / title.sh) there.
3. Automatically update settings.json with the correct absolute path using python/jq (safely parsing and inserting/updating JSON keys without breaking other settings).
4. Mark the target script as executable.

It also updates the README.md files (in the root and example directories) to present this as the recommended, one-command setup path, while preserving the manual configuration steps for advanced users.

Closes #74