fix(cli): researchclaw models config doesn't enable any provider

[arnml]

Issue

When running 'researchclaw models config', the CLI successfully saves provider configurations to ~/.researchclaw.secret/providers.json but doesn't enable any of them.

As a result, all providers have 'enabled': false, causing the app to report 'No model configured' even though providers are properly set up.

Root Cause

The configure_providers_interactive() function in src/researchclaw/cli/providers_cmd.py (lines 94-106) has a docstring saying 'set active' but the implementation never actually enables any provider.

Expected Behavior

After running 'researchclaw models config', at least one provider should be enabled/active so the app can function.

Solution Options

1. Automatically enable the first configured provider
2. Ask user which provider to make active during configuration
3. Both: ask during config and enable the selection