v0.3.1 — correct version in --version and User-Agent

Bugfix release. No functional change to any tool.

__version__ had been hard-coded to 0.1.0 since the first commit and was never bumped, while pyproject.toml moved on. Two consequences, both visible from outside and both present in 0.3.0:

• dspace-mcp --version reported 0.1.0, even in the package installed from PyPI as 0.3.0.
• The User-Agent header sent to every repository the server queries announced dspace-mcp/0.1.0.

The second one is why this is worth a release rather than a footnote. This server identifies itself deliberately, so that an instance administrator can see who is querying them and does not mistake it for an anonymous nuisance worth blocking by IP. A wrong version number undermines the point of that identification.

The version now comes from the installed package metadata, leaving pyproject.toml as the single source of truth — the same way the .mcpb packaging workflow already treats it. A test asserts the two stay in agreement, so this cannot drift again silently.

The defect predates 0.3.0; it surfaced while verifying that release against PyPI.