Disable prompt storage by default

[acunniffe]

Recently a few teams have shared that their secrets / PII scanners have been going off because their developers have been putting data into prompts that shouldn't be shared with the Coding Agents / LLMs / Git AI.

All the Git AI features that require raw prompts are experimental and limited in their usage, so we think it makes sense to disable prompt sharing by default and make it easy to turn back on per-repo.

This PR

• Toggles off prompt saving by default
• introduces git-ai config command to make it easier to update config.json
• Toggle off prompt saving in repos without remotes unless user has * for allowed repos
• Document git-ai config command in CLI reference

[git-ai-cloud-dev]

Stats powered by Git AI

🧠 you    █████████████████░░░  87%
🤖 ai     ░░░░░░░░░░░░░░░░░███  13%

More stats

• 0.0 lines generated for every 1 accepted
• 1 minute waiting for AI
• Top model: cursor::claude-4.5-opus-high-thinking (139 accepted lines, 4 generated lines)

AI code tracked with git-ai

[svarlamov]

Awesome work! Tested on my end and everything worked great -- just added two todos that we discussed in the PR description