Add provider guard to migrateSonnet1mToSonnet45() so it only runs for
firstParty (Anthropic) users. Without this, a 3P user with
model='sonnet[1m]' would have it rewritten to an Anthropic-specific
alias that is invalid for OpenAI/Gemini/Ollama providers.
Squash the current repository state back into one baseline commit while
preserving the README reframing and repository contents.
Constraint: User explicitly requested a single squashed commit with subject "asdf"
Confidence: high
Scope-risk: broad
Reversibility: clean
Directive: This commit intentionally rewrites published history; coordinate before future force-pushes
Tested: git status clean; local history rewritten to one commit; force-pushed main to origin and instructkr
Not-tested: Fresh clone verification after push
