Release OpenCode alpha.18 with terminal context cleanup

[hopeatina]

Release notes

• publish-ready version: @useorgx/orgx-opencode-plugin 0.1.0-alpha.18
• session.deleted clears the exact native session Wizard lease, owner-only context pack, pending activation, hydration cache, and runtime hydration
• project/session-derived paths are validated before deletion; unsafe or symlinked state fails closed
• terminal cleanup does not delete another native session state

Version and registry baseline

• package.json, package-lock root, and plugin.manifest.json are synchronized at 0.1.0-alpha.18
• the heartbeat version assertion is synchronized at 0.1.0-alpha.18
• npm alpha currently resolves to 0.1.0-alpha.17 with shasum 9586b227fd4878ff046abc91bbf8dcde9c7e1852
• npm latest remains on the pre-existing 0.1.0-alpha.7 tag; this prerelease targets the alpha channel
• this repository has no changelog file; this section follows its PR and GitHub release-note convention

Verification

• npm ci: 101 packages installed, 0 vulnerabilities
• npm run type-check
• npm test: 126 Vitest tests and 9 Node tests passed
• npm run build
• npm run pack: 83 files, 85.8 kB tarball, shasum e7963825e2d6f1f5021eed0f5cb26bbd050b0d5c
• focused terminal-path suite: 44 tests passed, including session A deletion without touching session B and a symlink non-deletion canary

Boundaries

• no merge performed
• no Git tag or GitHub release created
• no npm publish performed