#23040: Upgrade default Google model to Gemini 3.1 Pro and add Venice catalog entry

## Context Gemini 3.1 Pro (`gemini-3.1-pro-preview`) launched on 2026-02-19 with improved reasoning capabilities. The default model references in OpenClaw still point to `gemini-3-pro-preview`, meaning new installations and users who haven't pinned a specific model don't get the latest model. ## Changes - **`src/config/defaults.ts`**: update `gemini` alias from `google/gemini-3-pro-preview` to `google/gemini-3.1-pro-preview` - **`src/commands/google-gemini-model-default.ts`**: update `GOOGLE_GEMINI_DEFAULT_MODEL` to `google/gemini-3.1-pro-preview` - **`src/agents/venice-models.ts`**: add `gemini-3.1-pro-preview` entry to the Venice catalog with 1M context window and 65K max output tokens ## What's NOT changed - Users with explicit model config are unaffected - `gemini-flash` defaults remain on `gemini-3-flash-preview` (no 3.1 Flash released yet) - No changes to `normalizeGoogleModelId` (covered separately in #23034) <!-- greptile_comment --> <h3>Greptile Summary</h3> Updates default Gemini model references from `gemini-3-pro-preview` to the newly released `gemini-3.1-pro-preview` (launched 2026-02-19) across config defaults and command defaults. Adds the new model to the Venice catalog with 1M context window and 65K max output tokens. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The changes are straightforward model identifier updates across three files with consistent string replacements. The Venice catalog entry follows the exact pattern of the existing `gemini-3-pro-preview` entry. Tests already cover both model IDs, and the PR description clearly documents that users with explicit config are unaffected. - No files require special attention _{Last reviewed commit: 8a0fc13} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->