feat: add per-prompt model selection field

[mtibbits]

Summary

• Adds an optional model field to QueuedPrompt YAML frontmatter, allowing users to specify a Claude model ID (e.g. claude-haiku-4-5-20251001) per queued prompt
• When set, passes --model <id> to the claude CLI subprocess; when unset, behavior is unchanged (backward compatible)
• Includes R7 type-safe coercion in the YAML parser to handle YAML implicit typing (model: true → "True")
• Adds --model / -m flag to claude-queue add CLI command
• Surfaces model in claude-queue bank list output and template frontmatter

Changes

File	Change
models.py	model: Optional[str] = None field on QueuedPrompt
storage.py	R7 coercion in parse, round-trip in write, templates, bank list
claude_interface.py	--model flag injected before positional prompt arg
cli.py	--model/-m on add subparser, display in bank list

Test plan

• pytest tests/ -m "not llm_eval" — all 547 tests pass (verified locally)
• Verify claude-queue add "test" --model claude-haiku-4-5-20251001 creates prompt with model set
• Verify claude-queue add "test" (no flag) creates prompt with model=None
• Verify claude-queue template foo output includes model: null in frontmatter
• Verify claude-queue bank save foo && claude-queue bank list shows model field
• Verify round-trip: write prompt with model → parse → model preserved
• Verify YAML coercion: model: true in frontmatter → "True" string (invalid model, handled by CLI exit + retry)

🤖 Generated with Claude Code