Release v0.18.1: fix keys after dismissing questions

[oribarilan]

Release v0.18.1

Patch release containing the question-dismissal fix from #73 and documentation updates from #74.

Fixed

• Fixed Vim keys remaining unresponsive after dismissing or rejecting a question prompt (Rejecting a question prompt leaves vimcode stuck passing all keys through #72).

Changed

• Updated the documented cache-installed mode indicator limitation with the latest OpenCode and OpenTUI findings (mode indication #3).

Release preparation

• Updated package.json, src/version.ts, both README version pins, and changelog comparison links per CONTRIBUTING.md.
• just check passed: 313 tests, zero lint warnings or errors.
• Version consistency and git diff --check passed.

After CI passes, this PR must be squash-merged before tagging v0.18.1 and publishing the GitHub release.