Assistant parity: Lookup control in Table and Modify-structure wizards

[DDecoene]

Part of the v1.3.0 lookup feature. Design: docs/superpowers/specs/2026-07-10-lookup-columns-design.md (on release/v1.3.0). Required by the DoD Assistant-parity step; builds on the LOOKUP qualifier issue.

Scope

• TableWizard + ModStructWizard: per-column "Lookup…" control — pick a source table, a value column, an optional display column, or type a literal value list
• Emits the LOOKUP clause in the generated CREATE TABLE / ALTER TABLE
• Playwright: drive the wizard control in a real browser and assert the emitted command text + rendered REPL result

[DDecoene]

Merged in PR #67 (feature/62-wizard-lookup → release/v1.3.0). Assistant sidebar wizards now offer a Lookup control — this closes the v1.3.0 lookup-columns milestone (#58-#62).