feat: add MiniMax M2.7 to built-in catalog

[octo-patch]

Reason: Add MiniMax-M2.7 to the built-in MiniMax model catalog; MiniMax-M3 is present but the target model set requires both target model IDs.

This change:

• Adds the MiniMax-M2.7 catalog entry with its 204,800-token context window and text input support.
• Keeps reasoning controls unavailable for the always-on reasoning model.
• Adds a regression test covering both target MiniMax catalog entries.

Checks:

• jq -e . crates/core/models.json
• git diff --check
• cargo fmt --all -- --check
• cargo test -p devo-core --lib --no-default-features --features tokio/test-util builtin_minimax_catalog_contains_both_target_models
• cargo check -p devo-core --no-default-features
• Secret scan passed.