fix(interpreter): handle unclosed POSIX case patterns

[obinnanwachukwu1]

Fixes #301.

Summary

• scan shell character classes without mistaking an inner POSIX :], collating .], or equivalence =] terminator for the outer closing bracket
• preserve the Bash literal-[ fallback when the outer bracket is unmatched
• add a regression covering both the non-match and literal-prefix match behavior
• add a patch changeset

Verification

• pnpm --filter just-bash exec vitest run src/interpreter/control-flow.test.ts
• pnpm --filter just-bash test:comparison (560 passed)
• pnpm --filter just-bash test:unit (13,187 passed, 97 skipped)
• pnpm --filter just-bash build
• pnpm --filter just-bash typecheck
• pnpm --filter just-bash lint
• pnpm --filter just-bash knip

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