Update 2026-06-02 model inventory: add missing Gemini preview multipliers

[Copilot]

The 2026-06-02 inventory detected two new Gemini preview LLMs missing from model_multipliers.json, while alias coverage remained complete and unchanged. This PR adds those missing multiplier entries and locks them with a dated inventory regression test.

• Registry updates (both runtime sources)

  • Added the following multipliers to:
    • pkg/cli/data/model_multipliers.json
    • actions/setup/js/model_multipliers.json
  • New entries:
    • antigravity-preview-05-2026: 1.0
    • nano-banana-pro-preview: 0.2

• Inventory regression coverage

  • Added TestModelMultipliersInventoryUpdate20260602 in pkg/cli/effective_tokens_test.go.
  • Verifies both new model IDs resolve to expected multipliers from embedded registry data.

{
  "antigravity-preview-05-2026": 1.0,
  "nano-banana-pro-preview": 0.2
}

[Copilot]

Pull request overview

Adds two newly-detected Gemini preview model multipliers to both runtime registries and locks them with a dated regression test.

Changes:

• Add antigravity-preview-05-2026 (1.0) and nano-banana-pro-preview (0.2) to pkg/cli/data/model_multipliers.json.
• Mirror the same additions in actions/setup/js/model_multipliers.json.
• Add TestModelMultipliersInventoryUpdate20260602 to verify both entries load from embedded JSON.

Show a summary per file

File	Description
pkg/cli/data/model_multipliers.json	Adds the two new Gemini preview multiplier entries.
actions/setup/js/model_multipliers.json	Mirrors the new multiplier entries for the JS runtime.
pkg/cli/effective_tokens_test.go	Adds a dated regression test asserting both new multipliers load correctly.

Copilot's findings

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• Files reviewed: 3/3 changed files
• Comments generated: 0