Mirror the Build view into the file Explorer #10

Register the build-target tree a second time as fallout.buildExplorer, docked in the file Explorer and collapsed by default — so targets are reachable without leaving the Explorer for the Fallout container.

Implemented on feature/views-and-run-config (#2).

Approach

One provider instance, two view registrations. FalloutTargetsProvider is registered under both fallout.build and fallout.buildExplorer, so a single refresh() updates both homes and the two can never show different graphs.

Notes

• "visibility": "collapsed" so it doesn't push the file tree down for people who don't want it.
• Inline actions are shared via when clauses matching either view, rather than duplicated.

Depends on #9 for the view IDs.

Acceptance

• Build targets appear in the Explorer, collapsed by default
• Refresh updates both views from the one provider
• Run / Go to Definition work identically in both