feat: git-aware context tools

[TheArchitectit]

Summary

This PR adds five native, read-only git tools that replace ad-hoc bash invocations for common git operations: GitStatus, GitDiff, GitLog, GitShow, and GitBlame.

Problem

Before this change, the model had to use the generic bash tool for every git operation. This created several friction points:

Issue	Impact
Requires DangerFullAccess	Even read-only git commands need elevated permissions
Unstructured text output	Model must parse raw CLI output; brittle across git versions
Not discoverable	ToolSearch won't find "git diff" because no such tool exists
Inconsistent flags	Each bash invocation may use different formatting options
Wastes context window	Raw git log output with ANSI colors and padding consumes tokens

Solution

Five first-class tools with structured JSON output, ReadOnly permissions, and model-friendly descriptions:

Tool	Purpose	Key Parameters
GitStatus	Branch and working tree status	path (optional repo root)
GitDiff	Show changes between commits, or working tree vs index	staged, commit, path
GitLog	Commit history with filtering options	count, oneline, author, since
GitShow	Details for a specific commit	commit (hash or ref), stat
GitBlame	Line-level authorship for a file	path, start_line, end_line

All tools:

• Use PermissionMode::ReadOnly — safe in restricted environments
• Return structured JSON — no parsing required
• Are discoverable via ToolSearch with keywords like "git", "diff", "blame", "history"
• Include detailed doc comments explaining when to use the tool vs. generic bash

Implementation

• Added tool structs in rust/crates/tools/src/git.rs with ToolDescription derive macros
• Implemented run() for each tool using the existing git_stdout() helper
• Added comprehensive error handling for "not a git repo" and "file not found" cases
• All tools validate the target path is within the workspace sandbox

Test Plan

• GitStatus returns correct branch and file status JSON
• GitDiff with staged: true shows cached changes
• GitLog with count: 5 and oneline: true returns condensed history
• GitShow with a commit hash returns the diff and metadata
• GitBlame with a file path and line range returns per-line authorship
• All tools report clear errors when run outside a git repository
• All tools are listed by ToolSearch with relevant keywords
• Permission mode is ReadOnly for all five tools

Impact

• Safer: Read-only git operations no longer require DangerFullAccess
• More reliable: Structured output eliminates parsing brittleness
• More discoverable: Model can find and use git tools without being told they exist
• Token-efficient: JSON output is more compact than raw git CLI formatting
• Backward compatible: Existing bash git invocations continue to work