Feat: Add option to update Bundle in installation wizard

[SimonBlancoE]

Not sure if there's an existing alternative way to do this, but I don't know how else to apply the latest improvements after pulling from Main.

Right now, the installation wizard creates a backup of the existing bundle and goes all over the configuration, creating .env, asking for API keys, etc.

Wouldn't it be useful to add a non-destructive update option? It could have some of these features.

• Detect KAI specifically: Check for markers like skills/CORE/SKILL.md containing "Personal AI Infrastructure" (or add a version.txt) to avoid treating vanilla setups as updates.
• Pre-fill configuration: Load existing values from .env/settings.json to use as defaults in prompts, avoiding re-entry of unchanged settings.
• Merge files intelligently: For Markdown files and .env, parse and merge new template content while preserving user-added sections or custom variables.
• Add CLI flags: Support --update (selective merge, no full backup), --force-fresh (current behavior), and --dry-run (preview changes).
• Track versions: Write a .kai-version file on install and use it to apply targeted patches during updates.