feat: Phase 1 code-agent capabilities — file_edit, git tools, parallel execution, tool output preview

New tools:
- file_edit: surgical line-range or pattern edits (yolo only)
- git_status: show changed files (read-only)
- git_diff: show unstaged/staged diff (read-only)
- git_log: show recent commits (read-only)

Agent improvements:
- parallel execution for independent read-only tool calls
- mutating tools (file_write, file_edit, shell_run) run sequentially
- tool output preview in logs with [output] marker

TUI improvements:
- tool cards now show truncated output preview (up to 8 lines)
- mergeToolLog updates placeholder cards with results
- toolStatusText keeps activity bar single-line

Documentation:
- README updated with git tools and file_edit descriptions

README.md

@@ -125,6 +125,9 @@ Read-only tools are available by default:
 - `file_list`
 - `file_search` with optional `context_lines` and `max_results`
 - `code_symbols` for Go packages, imports, types, functions, and methods
+- `git_status` shows changed files
+- `git_diff` shows unstaged or staged diff output
+- `git_log` shows recent commit history
 
 Web tools are also available in read-only mode:
 
@@ -133,8 +136,9 @@ Web tools are also available in read-only mode:
 
 `--yolo` additionally enables:
 
-- `file_write`
-- `shell_run`
+- `file_write` for creating or replacing whole files
+- `file_edit` for surgical line-range or pattern edits to existing files
+- `shell_run` for non-interactive shell commands
 
 Use `--yolo` for prompts that ask agentu to run or inspect local commands, for
 example:
@@ -143,6 +147,8 @@ example:
 请帮我运行 `go test ./...` 并总结结果
 ```
 
+
+
 ## Development
 
 Run the verification suite: