Provision ANTHROPIC_API_KEY for default SIA live runs

[micahstubbs]

Board issue: sia_rust-e2j.2

Finding

The local environment does not define ANTHROPIC_API_KEY. That blocks the default live SIA path: src/config.rs defaults to default-meta / default-target and agent_impl = "claude"; src/profiles.rs resolves both default profiles to the Anthropic provider; src/agent_impls/claude.rs then calls messages_transport_for(None), which reads ANTHROPIC_API_KEY directly.

Code path

• src/bin/sia.rs:30 loads .env before config/provider reads.
• src/config.rs:54 and src/config.rs:66 set the default profiles and Claude runner.
• src/profiles.rs:161 and src/profiles.rs:170 cover the default Anthropic meta/target profiles.
• src/agent_impls/claude.rs:34 and src/llm/provider_mapping.rs:117 require ANTHROPIC_API_KEY.
• docs/CREDENTIALS.md:8 says the default meta/feedback agent talks to Anthropic.

Acceptance criteria

• Add a valid Anthropic API key to secure local/team secret storage and the runtime environment as ANTHROPIC_API_KEY.
• Do not commit the secret value or paste it into GitHub.
• Verify with either a minimal default cargo run --features llm -- run ... or the relevant ignored live Anthropic tests, and attach only non-secret output.