fix(volcengine): update default doubao embedding model

[qin-ctx]

Description

Update default Doubao embedding model references to doubao-embedding-vision-251215 across user-facing configuration examples and cloud setup defaults.

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Refresh README, contributing guides, FAQ/getting-started/configuration docs, and example configs to use doubao-embedding-vision-251215
• Update Helm/example values and local evaluation dataset snippets so generated sample configs stay consistent with the supported Volcengine embedding model
• Change the cloud setup wizard default embedding model and align telemetry usage tests; pre-commit also reformats openviking_cli/setup_wizard.py

Testing

• Ran python -m pytest --override-ini addopts='' tests/models/test_embedding_telemetry_usage.py
• Reviewed the staged diff to confirm the updated model ID is consistent across docs, examples, and defaults
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

• ruff format reformatted openviking_cli/setup_wizard.py during the commit hook.

[github-actions]

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⚡ Recommended focus areas for review Documentation Inconsistency Release date for doubao-embedding-vision-251215 is listed as 2025-06-15, which mismatches the model's date suffix (251215 = 2025-12-15). | Doubao-Embedding-Vision | `doubao-embedding-vision-251215` | 2025-06-15 | Documentation Inconsistency Release date for doubao-embedding-vision-251215 is listed as 2025-06-15, which mismatches the model's date suffix (251215 = 2025-12-15). | Doubao-Embedding-Vision | `doubao-embedding-vision-251215` | 2025-06-15 |

[github-actions]

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[ZaynJarvis]

lgtm