[datlechin]

Summary

• New sheet, Database > Build Join Query…: pick tables, each joins the earlier ones on the cheapest chain of foreign keys.
• A junction table between a many-to-many pair is added automatically; a junction or chain wins over two tables that only share a parent.
• A table no key reaches is cross joined, and the sheet says so.
• Per table: Inner or Left Join, and a picker of every key to an earlier table, or none.
• Column checkboxes replace SELECT *.
• Filters reuse the filter bar's operators and FilterSQLGenerator, so values are typed and escaped the same way.
• Live SQL preview, quoted by the connection's driver; tables outside the engine's implicit schema are schema-qualified, as the browse query does.
• Open in Query Tab writes the SQL into a new query tab on that database.
• ER diagram: Command- or Shift-click adds a table to the selection.
• ER diagram: the new toolbar button, or Build Join Query… in a table's or column's context menu, opens the builder on the selection.
• The menu item sits after Open Table and Show Structure, so destructive items stay last; a right-click inside a multiple selection keeps it.
• With the diagram focused, the Database menu command uses the diagram's selection (responder chain); otherwise the sidebar's selected tables.
• ER selection is an ordered list instead of one optional id; tests that built a scene with selectedNodeId: now pass selectedNodeIds:.
• Keys spelled in another case than the catalog (SQLite reports parent(id) for table Parent) resolve to the catalog name; the ER diagram dropped that edge before.
• The ER diagram no longer draws a key into another schema to a same-named table of its own schema.
• Enabled for engines with SQL and foreign keys; off in Agent mode like the other browse commands.
• Docs: docs(features): document the join builder docs#113

Test plan

• JoinGraphTests, JoinQueryDraftTests, JoinQuerySQLWriterTests: paths, relinking, SQL per dialect, LEFT and CROSS joins, columns, WHERE escaping, schema qualification.
• JoinBuilderOpeningTests: new tab on the builder's database, sidebar seeding keeps one schema.
• ERDiagramPointerInputTests: Command/Shift-click, right-click menu, disabled command, multi-selection accessibility. Its fixture offers no join builder unless a test asks, so the diagram menu tests keep their expectations.
• ERDiagramGraphBuilderTests, ERDiagramViewModelLoadTests, ForeignKeyTargetScopeTests: case-mismatched reference keeps its edge, key into another schema is not drawn.
• MainMenuBuilderTests: menu enablement.
• UI: JoinBuilderUITests picks album and artist on the fixture's diagram and reads the join on album.artist_id = artist.id, quoted the SQLite driver's way, in the new tab.

Screenshots

No join builder existed before.

Fixes #2531