Release gate: nothing has consumed the driver as a published artifact #10

The gap

The V1 plan's release gate asks for the driver to be consumed by at least two projects outside
this repository before a non-snapshot release. Nothing has ever depended on it as a Maven
artifact — every test to date builds it in the same reactor, which does not exercise the thing
a consumer actually hits:

• whether the POMs resolve from a repository rather than from target/
• whether the BOM does what a BOM should when imported
• whether declaring exactly one platform package yields a working driver, and what the error
  looks like when someone declares none or the wrong one
• whether a 167 MB artifact uploads and downloads intact
• whether the native extraction path behaves when the jar comes from ~/.m2 rather than from a
  build directory

What would close this

1. Publish a snapshot to Central's snapshot repository. This is the cheap part and is worth
   doing before any of the release polish, because it is the only way to find out whether the
   above works.
2. Have two projects consume it. Candidates worth asking: a chDB cookbook example, the ADBC
   driver work, or any internal tool that wants an embedded analytical engine from the JVM.
3. Record what broke. The value of this gate is the list of things that only fail when
   consumed, and that list does not exist yet.

Blocked on

Publishing prerequisites, tracked separately: the org.chdb namespace claim (unclaimed today;
needs a DNS TXT record on chdb.org), GPG signing, and the POM metadata Central requires.
See docs/release-readiness.md on the v1/close-test-gaps branch.