CLI --version reports 0.2.0 while package is 0.3.0; --help omits agentic mode

[williamzujkowski]

src/cli.ts:121 hardcodes the version string nexus-eval-livecodebench 0.2.0, but package.json is at 0.3.0. Because the string is hardcoded, it drifts on every release.

Fix: Read the version from package.json at runtime (e.g. import the JSON, or inject process.env.npm_package_version at build) so --version is always correct.

While here, the --help notes block (src/cli.ts:81-87) still only describes v0.1/v0.2 model-only and v0.2 test-runner behavior and does not mention the v0.3 --agentic-mode that the same help text documents in the options list. Update the notes to reflect v0.3.