feat: add config file support and optional toolchains

[shrwnsan]

Summary

• Add ~/.agentbox/config file for persistent settings (bash key=value format)
• Add --no-java flag to exclude Java toolchain (default: included for backwards compatibility)
• Add --no-opencode flag to exclude OpenCode installation (default: included)
• Add --cc-latest flag for Claude Code latest channel (default: stable)
• Fix Java status message to show friendly "excluded" text instead of command-not-found error
• Auto-enable OpenCode when AGENTBOX_TOOL=opencode is set, overriding AGENTBOX_INCLUDE_OPENCODE=false

Configuration

Config file supports bash syntax with shebang for editor syntax highlighting:

#!/bin/bash
# ~/.agentbox/config

AGENTBOX_TOOL=claude
AGENTBOX_INCLUDE_JAVA=false
AGENTBOX_INCLUDE_OPENCODE=false
AGENTBOX_CC_CHANNEL=latest

CLI flags override config file settings.

Examples

# Use config file defaults
~/.agentbox/agentbox --model glm-4.7

# Override config with CLI flags
~/.agentbox/agentbox --no-java --cc-latest --model glm-4.7

# Config file with all options
cp config.example ~/.agentbox/config

Benefits

• Users can set preferred defaults without typing flags every time
• Backwards compatible: Java and OpenCode still included by default
• Smaller images possible with --no-java and --no-opencode
• Latest Claude Code accessible via --cc-latest flag
• Tool selection (opencode) automatically includes required installation, even if config has AGENTBOX_INCLUDE_OPENCODE=false

🤖 Generated by Claude Code - GLM 4.7

[shrwnsan]

Closing in favor of new PR #54 with clean history