feat: Add Gemini support (#145)

This PR introduces support for Google's Gemini as a new AI assistant in
Claude Squad.

### Changes

- **Gemini Integration:**
- The application can now detect and use the `gemini` command-line tool
if it's available on the user's system.
- Tmux sessions are now configured to properly handle Gemini's prompts
and output.
- **Documentation:**
- The `README.md` has been updated to include instructions on how to use
Gemini with `cs`.
- `CONTRIBUTING.md` now includes a guide for adding new AI assistants in
the future.

This allows users to leverage Gemini's capabilities within the existing
Claude Squad workflow, expanding the tool's versatility.

Author: fijimunkii

README.md

@@ -1,6 +1,6 @@
 # Claude Squad [![CI](https://github.com/smtg-ai/claude-squad/actions/workflows/build.yml/badge.svg)](https://github.com/smtg-ai/claude-squad/actions/workflows/build.yml) [![GitHub Release](https://img.shields.io/github/v/release/smtg-ai/claude-squad)](https://github.com/smtg-ai/claude-squad/releases/latest)
 
-[Claude Squad](https://smtg-ai.github.io/claude-squad/) is a terminal app that manages multiple [Claude Code](https://github.com/anthropics/claude-code), [Codex](https://github.com/openai/codex) (and other local agents including [Aider](https://github.com/Aider-AI/aider)) in separate workspaces, allowing you to work on multiple tasks simultaneously.
+[Claude Squad](https://smtg-ai.github.io/claude-squad/) is a terminal app that manages multiple [Claude Code](https://github.com/anthropics/claude-code), [Codex](https://github.com/openai/codex), [Gemini](https://github.com/google/generative-ai-docs) (and other local agents including [Aider](https://github.com/Aider-AI/aider)) in separate workspaces, allowing you to work on multiple tasks simultaneously.
 
 
 ![Claude Squad Screenshot](assets/screenshot.png)
@@ -82,6 +82,7 @@ cs
 - Launch with specific assistants:
    - Codex: `cs -p "codex"`
    - Aider: `cs -p "aider ..."`
+   - Gemini: `cs -p "gemini"`
 - Make this the default, by modifying the config file (locate with `cs debug`)
 
 <br />

session/tmux/tmux.go

@@ -22,6 +22,7 @@ import (
 const ProgramClaude = "claude"
 
 const ProgramAider = "aider"
+const ProgramGemini = "gemini"
 
 // TmuxSession represents a managed tmux session
 type TmuxSession struct {
@@ -128,7 +129,7 @@ func (t *TmuxSession) Start(workDir string) error {
 		return fmt.Errorf("error restoring tmux session: %w", err)
 	}
 
-	if t.program == ProgramClaude || strings.HasPrefix(t.program, ProgramAider) {
+	if t.program == ProgramClaude || strings.HasPrefix(t.program, ProgramAider) || strings.HasPrefix(t.program, ProgramGemini) {
 		searchString := "Do you trust the files in this folder?"
 		tapFunc := t.TapEnter
 		iterations := 5
@@ -220,6 +221,8 @@ func (t *TmuxSession) HasUpdated() (updated bool, hasPrompt bool) {
 		hasPrompt = strings.Contains(content, "No, and tell Claude what to do differently")
 	} else if strings.HasPrefix(t.program, ProgramAider) {
 		hasPrompt = strings.Contains(content, "(Y)es/(N)o/(D)on't ask again")
+	} else if strings.HasPrefix(t.program, ProgramGemini) {
+		hasPrompt = strings.Contains(content, "Yes, allow once")
 	}
 
 	if !bytes.Equal(t.monitor.hash(content), t.monitor.prevOutputHash) {