chore(release): bump workspace version to 0.3.1

Cargo.toml had drifted behind the v0.3.0 tag (stuck at 0.2.0) -- the
project's own release.yml comment warns this silently defeats
scripts/mcp-launcher.sh's verified-download fast path for anyone on a
checkout between releases, comparing a stale local version against the
downloaded binary's real one and falsely treating it as corrupted.
Bumping now, ahead of tagging v0.3.1 for the docs/fix changes in the
previous two commits.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: Your Name

Cargo.lock

@@ -17,7 +17,7 @@ members = [
 # version against the downloaded release binary's real `--version` output
 # and treats any mismatch as a corrupted/wrong download, so a stale value
 # here silently defeats the verified-download fast path for everyone.
-version = "0.2.0"
+version = "0.3.1"
 edition = "2024"
 license = "MIT"
 rust-version = "1.85"