feat: inject git context into chat prompt

[owainlewis]

Summary

• add a dynamic git context system-prompt block at session start with branch, status, and recent commits
• degrade silently when the session cwd is outside a git repo
• cover repo and non-repo behavior in tests and update generated developer docs

Closes #63

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Disable repo-controlled hooks for git status

When Neo starts in a repo whose local config sets core.fsmonitor, this new git status --short call invokes that fsmonitor hook immediately, before the model/tool permission policy has a chance to gate command execution. That means simply opening chat in such a repository can run arbitrary local code from git configuration; please force unsafe repo-controlled integrations off for this automatic snapshot (for example by overriding fsmonitor for the command or avoiding status) before collecting git context.

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