fix(sidebar): use grouped form layout in favorite edit dialogs

[datlechin]

Problem

The New Favorite / Edit Favorite sheet rendered with a large empty region on the left, labels pushed to mid-dialog, and fields crushed against the right edge.

Root cause

The form used .formStyle(.columns), which lays out one shared trailing-aligned label column for the whole form. The dialog put the ~90-character ";;" hint sentence (and the keyword error text) into the label slot of an empty LabeledContent. That single row inflated the shared label column, which right-aligned every short label toward the center and squeezed the value column into a narrow strip. The same anti-pattern was copy-pasted into LinkedFavoriteMetadataDialog.

Changes

• Rebuilt both dialogs on the repo-standard sheet shape (title row, Divider, Form with .formStyle(.grouped), Divider, bottom-right Cancel/primary row). This matches the 24 existing .grouped form sites, Apple's grouped-form guidance (WWDC22 10052, Food Truck sample), and HIG rules for sheets, text fields, and toggles.
• The Query editor is now a full-width TextEditor in its own section (minHeight 180, monospaced), with the ";;" hint as a real section footer.
• Keyword validation shows inline directly under the Keyword field. Global is a checkbox (HIG: do not replace a checkbox with a switch) with a visible "Available in all connections" caption instead of a hover tooltip.
• Extracted the duplicated keyword validation from both view structs into SQLFavoriteEditValidation.swift (SQLFavoriteKeywordValidator pure classifier plus SQLFavoriteKeywordField with an injectable availability check). This also fixes a latent race: an in-flight availability check could overwrite the result of a newer synchronous validation. Every validate call now invalidates stale checks.
• Removed a latent perf issue: isValid trimmed the full query string (up to 500KB) on every body evaluation. It now uses a short-circuiting blank check. The 500KB save cap is unchanged.
• CreateDatabaseSheet keeps .formStyle(.columns) on purpose: all its labels are short and it is not affected.

Tests

• New SQLFavoriteEditValidationTests: classifier table (empty, space, unavailable, reserved-keyword shadow), warning-allows-save vs error-blocks-save semantics, keyword trimming, and a deterministic stale-response race test using gated AsyncStreams.
• No UI automation added: TableProUITests has no harness for driving a .sheet(item:) dialog and no storage-injection seam, so the keyword-validation flow cannot run deterministically against the live SQLite-backed store. The extracted logic carries the coverage instead.
• swiftlint lint --strict clean on all changed files.

Follow-up

The screenshots in docs/features/favorites.mdx (sql-favorite-create.png, sql-favorite-create-dark.png) show the old layout and need recapturing. The page text stays accurate.