fix: skip Python/Go tools installation when not available

Issue:
- Script tried to use python3/go before they were installed
- 'bash: python3: command not found'
- 'bash: go: command not found'
- Caused errors even though script continued

Root Cause:
- Python tools section ran unconditionally
- Go development tools section ran unconditionally
- Assumed Python/Go were already installed

Fix:
1. Python tools:
   - Wrap in: if command -v python3 &> /dev/null
   - Skip with message if Python not available
   - Only install grpcio, protobuf, etc. when Python exists

2. Go development tools:
   - Wrap in: if command -v go &> /dev/null
   - Skip with message if Go not available
   - Only install protoc-gen-go, golangci-lint when Go exists

Behavior:
Before:
[INFO] Installing/updating Python development tools...
bash: python3: command not found
[SUCCESS] Python tools ready  # ❌ Misleading

After:
[SKIP] Python not available, skipping Python development tools
[SKIP] Go not available, skipping Go development tools

Benefits:
✅ No confusing error messages
✅ Clear skip messages for missing tools
✅ Script continues gracefully
✅ Tools installed later when Go/Python are available
✅ Works in ultra-minimal base images

Note: Your Dockerfile includes Go/Python via mise, so this
won't affect normal usage. This adds resilience for testing
in bare-bones environments.