feat(datagrid): native dropdown picker for ENUM and SET cells (#1283)

[datlechin]

Summary

• Native NSMenu dropdown picker for ENUM and SET columns, triggered by the cell chevron. Closes Enum type dropdown select #1283.
• Drivers (MySQL, MariaDB, PostgreSQL, ClickHouse, DuckDB, MongoDB JSON-schema) populate allowed values directly in PluginColumnInfo.allowedValues instead of being parsed downstream from the type string.
• Filter rows show an enum picker for = and != operators on enum columns.

Behavior

Trigger	Action
Click chevron	Opens native NSMenu picker (single-select for ENUM, multi-select with Cmd+click for SET)
Double-click cell body	Opens text overlay editor (typing a freeform value is still possible; server rejects if invalid)
Return on focused cell	Text overlay (existing behavior)

Matches Apple HIG: chevron = explicit "pick from list", cell body = "type/correct" affordance, both available for different intents.

Edge cases handled

• Nullable column → italic NULL sentinel at top, separated.
• Drift value (current cell value not in declared enum) → appended after a separator with exclamationmark.triangle.fill and localized tooltip.
• Default value pre-highlighted on empty/new-row cells.
• Very narrow column → text truncates with ellipsis, chevron hides if it can't fit at all; no text/chevron overlap.

Driver scope

Engine	Discovery source
MySQL / MariaDB	COLUMN_TYPE ENUM(...) / SET(...) parsed in driver
PostgreSQL	pg_type + pg_enum joined in fetchColumns
ClickHouse	system.columns.type Enum8('v'=1, ...) parsed in driver (handles Nullable(...) / LowCardinality(...))
DuckDB	duckdb_types() WHERE type_category = 'ENUM'
MongoDB	options.validator.$jsonSchema.properties.<col>.enum
SQLite	Existing CHECK (col IN (...)) DDL parser retained as fallback

PostgreSQL was the most visible gap before — pg_enum data existed but never reached the picker. SQLite/MSSQL/Oracle CHECK-constraint expansion is intentionally out of scope.

Architecture changes

• PluginColumnInfo grows optional allowedValues: [String]? (Codable shape change, no PluginKit ABI bump — JSON encoded, missing key decodes to nil).
• MainContentCoordinator.fetchEnumValues shrinks from per-engine orchestration to col.allowedValues lookup + SQLite CHECK fallback.
• ColumnType.parseEnumValues / parseClickHouseEnumValues deleted; moved to EnumValueParser in TableProPluginKit so drivers parse at fetch time.
• FieldEditorResolver moved from Views/RightSidebar/FieldEditors/ to Views/Shared/FieldEditors/.
• DataGridCoordinator.rebuildKindSets now trusts columnEnumValues instead of ct.isEnumType (the classifier only sees the raw type name and can't recognize PG UDTs).
• EnumPopoverContentView (SwiftUI) deleted, replaced by EnumMenuPicker (AppKit NSMenu).
• Cell drawing now clips to bounds and handles the "too narrow for ellipsis" case cleanly.

Plugin re-release

No PluginKit ABI bump needed. DuckDB and MongoDB plugins should get patch tags (plugin-duckdb-v1.0.10, plugin-mongodb-v1.0.10) after merge to main, since their code (not just data shape) changed.

Test plan

• MySQL: ENUM and SET column cells show chevron, picker opens on click, multi-select works for SET
• PostgreSQL: CREATE TYPE foo AS ENUM(...) column shows picker (was broken before this PR)
• ClickHouse: Enum8('a'=1, 'b'=2) and Nullable(Enum8(...)) both work
• DuckDB: CREATE TYPE foo AS ENUM(...) column shows picker
• MongoDB: collection with $jsonSchema.properties.col.enum shows picker
• SQLite: CHECK (col IN ('a','b')) regression check — still works via fallback
• Nullable column shows NULL sentinel at top of menu
• Filter panel: = and != on enum column shows picker instead of text input
• Right sidebar field editor for enum still works (existing behavior)
• Narrow column: text truncates cleanly with ellipsis, no overflow into next column
• Very narrow column: chevron hides, no chevron/text overlap
• Double-click cell body opens text overlay (not picker)
• swiftlint lint --strict passes
• xcodebuild test passes