Add provider selection picker command

[404pilo]

Summary

Add a :AICommitSelectProvider command that displays a picker allowing users to switch between configured AI providers.

Motivation

• Quick switching between providers without editing configuration
• Test different providers on the same commit
• Use cheaper models for simple commits, premium models for complex ones
• Better developer experience for multi-provider setups

Proposed Implementation

Command

:AICommitSelectProvider

UI Behavior

• Reuse existing picker UI style (ui/picker.lua)
• Display list of available providers from providers.list()
• Show enabled/disabled status for each provider
• Highlight currently active provider
• Same keybindings: j/k navigate, Enter select, q cancel

Provider Selection Scope

Two options to consider:

Option 1: Session-scoped (simpler)

• Use config.set("active_provider", selected)
• Applies for current Neovim session only
• Reverts to configured default on restart

Option 2: Persistent across sessions

• Save selection to ~/.local/share/nvim/aicommits-provider.json
• Load on plugin initialization
• Override configured default until changed again
• More complex but provides true persistence

Example Picker Display

 Select AI Provider

 ● openai (gpt-4.1-nano)
   anthropic (claude-3-5-haiku-20241022)
   vertex (gemini-2.0-flash-lite)

 [Enter] Select   [q] Cancel   [j/k] Navigate

Acceptance Criteria

• :AICommitSelectProvider command implemented
• Picker displays all registered providers
• Shows current active provider indicator
• Selection updates active_provider config
• Decide on session-scoped vs persistent behavior
• Works with existing picker UI style
• Handles case where no providers configured
• Tests for provider switching
• Documentation in README

Technical Notes

• Provider registry: lua/aicommits/providers/init.lua
• Existing picker: lua/aicommits/ui/picker.lua
• Config management: lua/aicommits/config.lua (set() method)
• Could display provider config (model name) in picker for context

Related

• Provider system: feat: extensible AI provider system for multiple API support #2
• Future providers: Add Anthropic Claude provider support #4 (Anthropic), Add Google Vertex AI provider support #5 (Vertex)