Installer: fix hardcoded paths and model provider requirements

[NOVA-Openclaw]

Problems

1. ANTHROPIC_API_KEY hard-requirement

The shell-install.sh checks for ANTHROPIC_API_KEY and warns/blocks if not found. But agents using OpenRouter or other providers don't need a direct Anthropic key. The installer should:

• Check for ANY configured LLM provider key (ANTHROPIC_API_KEY, OPENROUTER_API_KEY, OPENAI_API_KEY)
• Only warn if NO provider key is found at all
• Not hard-require a specific provider

2. Hardcoded log path in output

The installer's "Next steps" output includes:

tail -f ~/clawd/logs/memory-extract-hook.log

This references the deprecated ~/clawd/ path. Should use $OPENCLAW_WORKSPACE or a relative path.

3. Empty ANTHROPIC_API_KEY in config

On both staging and Newhart's environments, ANTHROPIC_API_KEY was set to empty string "" in openclaw.json env.vars. The installer should treat empty string same as missing, and not write empty strings to config.

Current Behavior

• Installer exits early if ANTHROPIC_API_KEY not found in env or config
• Even when OPENROUTER_API_KEY is present and all models use openrouter/

Expected Behavior

• Installer checks for at least one LLM provider key
• Warns but continues if a specific provider key is missing
• Uses relative/env-based paths in all output messages