Part of epic #3602.

Scope

Add a new menu option to zeph init's LLM provider selector that pre-fills a [[llm.providers]] type = \"compatible\" name = \"gonkagate\" entry.

Files to modify

• src/init/llm.rs:45 — extend the providers array with \"Gonka (decentralized — via GonkaGate)\" at index 5; add a new match arm that:
  • Sets state.provider = Some(ProviderKind::Compatible)
  • Sets state.compatible_name = Some(\"gonkagate\".into())
  • Sets state.base_url = Some(\"https://api.gonkagate.com/v1\".into())
  • Offers a model picker (default Qwen/Qwen3-235B-A22B-Instruct-2507-FP8, plus custom... escape hatch)
  • When vault_backend != \"age\", prompts for the gp-... API key via Password
  • When vault_backend == \"age\", prints instructions to run zeph vault set ZEPH_COMPATIBLE_GONKAGATE_API_KEY gp-... after wizard completion
• Update the secrets-instructions printer to mention the gonkagate key.

Acceptance

• Running cargo run --features full -- --init and selecting the new option produces a valid [[llm.providers]] block.
• cargo +nightly fmt --check, cargo clippy --workspace --features full -- -D warnings, cargo nextest run --workspace --features full --lib --bins all green.
• Existing wizard tests in src/init/ updated; one new unit test asserts the rendered TOML matches expectations.
• CHANGELOG.md [Unreleased] updated.

Depends on

None.

Size

S (~1.5h)