Share one package-version constant and test the MCP handshake version

[coderyaz856]

Follow-up to #11

Context

Issue #11 identified that the MCP client reported the hardcoded version 3.1.0 instead of the installed package version.

Since this pull request was opened, PR #14 updated main so that the MCP client reads its version from package.json. After rebasing onto the latest main, this pull request is now a cleanup and regression-testing contribution.

Change

• Export PACKAGE_VERSION from lib/utils/package-root.js.
• Use that shared constant in both bin/mantis.js and lib/impl/mcp-client-service.js.
• Remove the duplicated package.json reading logic.
• Add a regression test that captures the MCP initialize request and verifies that clientInfo.version matches the package version.

This gives the CLI and MCP client one source of truth for the package version and protects the handshake behavior against regression.

Testing

• node --test: 22 of 22 tests pass.
• The test suite includes the latest upstream drive-command tests.
• node bin/mantis.js --version returns 3.7.0.
• node bin/mantis.js --help works correctly.
• git diff --check origin/main...HEAD passes.
• PR rebased onto commit 8a5163a with no remaining conflicts.

Scope

No commands, configuration, authentication behavior, MCP headers, URLs, or user-facing output are changed.

[coderyaz856]

@MantisCartography Please review this change