feat: label free models in OpenCode - #211

Changes

• Append (Free) to V1/V2 model display names when all catalog prices, including cache and context tiers, are zero; retain existing Free labels.
• Keep model IDs, routing, and generated catalogs unchanged.
• Remove project-level model defaults so user preferences apply.

Verification

• 245 unit tests; lint, formatting, typechecking, and build passed.
• Regression tests cover paid tiers/caches, existing labels, word boundaries, and V1/V2 parity.
• Docker smoke tests on OpenCode V1.19.3 and V2.0.27 confirmed free/paid display names, unchanged wire IDs, and successful free-model requests. The final suffix-boundary refinement does not affect the tested catalog names.
• Desktop GUI rendering was not directly checked. This is a display-name suffix, not a native badge; provider logo support is out of scope.