feat: fix model nits

[k11kirky]

Problem

Model IDs in the ACP connection configuration options display with provider prefixes (e.g., "anthropic/claude-3-sonnet") instead of user-friendly names, making them harder to read in the UI.

Changes

• Added formatModelId function to strip provider prefixes from model IDs for display purposes
• Updated ACP connection adapter to format model option names using the new function while preserving original values
• Improved type definitions for model options and groups with proper TypeScript interfaces
• Fixed model sanitization logic to only apply default gateway model when not using codex adapter
• Removed unused close capability from Claude agent initialization

How did you test this?

Manual testing of model selection UI to verify that model names display without provider prefixes while maintaining correct functionality for model selection and filtering.

closes: #1320

[k11kirky]

• feat: fix model nits #1376 👈 (View in Graphite)
• main

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