Add ER diagram position persistence and layout configuration

[luis100]

Summary

• Position persistence: Node positions are saved automatically to localStorage after each drag and restored on page load — the layout survives refresh and browser restarts. Physics is disabled immediately when all positions are available; when new tables are added, previously positioned nodes are pinned while physics settles the new ones, then the full layout is saved.
• Configuration dropdown: A "Configuration ▾" button in the Schema card header opens a popup menu with three layout actions: Upload layout, Download layout (erdiagram-layout.json), and Reset layout. The download/upload format is identical to the localStorage format ({tableId: {x, y}}), making it ready for future server-side sharing.
• Dev mode fixes: <collapse-all-properties/> commented out in Server.gwt.xml (fixes per-file compilation error in the GWT code server); solr-solrj-jetty excluded from the codeserver classpath (fixes Jetty version conflict on startup).

Test plan

• Open ER diagram, drag nodes around — positions should persist after page refresh
• Open ER diagram with no saved layout — physics runs and stabilises normally; first drag saves the layout
• Download layout, reset, then upload the downloaded file — diagram should restore the saved positions
• Reset layout — physics reruns from scratch, localStorage entry is cleared
• Run mvn -f dev/codeserver gwt:codeserver -Pdebug-server -DprojectPath=$(pwd) — should start without errors

🤖 Generated with Claude Code

[luis100]

The CI test failures are pre-existing on the development branch and are not introduced by this PR.

Confirmed locally: running DefaultJobContextTest and ConfigurationIntegrityValidatorTest against a clean checkout of development (before our changes) produces the same 4 failures:

• ConfigurationIntegrityValidatorTest.testBlockDeletionOfVirtualTableUsedByDenormalization
• ConfigurationIntegrityValidatorTest.testBlockDeletionOfVirtualColumnUsedByVirtualFK
• ConfigurationIntegrityValidatorTest.testBlockModificationOfVirtualColumnUsedByVirtualFK
• DefaultJobContextTest.testConstructorThrowsBatchJobExceptionWhenDenormalizationConfigFailsToLoad

All four are in server-side batch/validation logic. This PR only touches client-side GWT UI, CSS, the GWT module descriptor, and the dev codeserver pom.