Delete @deepseek-ai/dsh-invariants, every package's ./invariant companion
and its tests, the invariant gates and Vitest setup, the scoped-event
resolver generator, and the INVARIANT-coded listener rethrow paths.
Update docs, READMEs, Agent Notes, and add an upgrade guide.
Shell discovery keyed entries by resolved path. On merged-/usr hosts the
login shell /bin/bash from $SHELL and the PATH hit /usr/bin/bash for the
`bash` candidate are one file with two spellings, so the menu showed
"bash" twice. Key discovered shells by executable name, compared without
letter case or `.exe`, and keep the earliest entry so the default shell
stays first.
Tianyi Cui