Adds two enum-style column types where the column declares a fixed set of
options (stable id + name + palette color) and every cell is constrained to
them.

- COLUMN_TYPES gains `select` / `multiselect`; SELECT_COLORS is a fixed,
  theme-aware palette mapping 1:1 to Badge color variants (no raw hex)
- ColumnDefinition.options carries the option set. Cells store option *ids*
  (a string for select, string[] for multiselect) so renaming or recoloring
  an option never rewrites row data
- Row validation enforces membership; coercion tolerantly maps an option
  *name* to its id for tool/import writes and drops unmatched entries
- validateColumnDefinition enforces non-empty, unique-id, unique-name and
  valid-color option sets, and rejects options on non-select columns
- Contract gains selectOptionSchema plus a cross-field refine requiring
  options exactly on select types; routes thread options through type
  changes and a new options-only updateColumnOptions path

No migration: column config already lives in the user_table_definitions
schema JSONB blob.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014e4MvFV1szLhNLap1CCNUd

Addresses review findings on the select/multiselect column types:

- Column type conversion now checks each existing value against the target
  option set (resolve by id or name); a `select`/`multiselect` change is
  blocked when values don't fit, instead of accepting shapes that later
  coercion would strand or silently drop
- Inline select editor discards its draft on Escape (matching the text/date
  editors) rather than committing on menu close
- A required single-select no longer offers "None" — clearing to null could
  never be committed

Exports resolveSelectOptionId from validation for the conversion gate.

Round 2 review fixes:

- A required multiselect can no longer be emptied — the toggle that would
  remove the last option is ignored, since an empty selection can't be
  committed (server rejects it). Mirrors the required single-select "None"
  guard.
- Inline cell save now compares old vs new value structurally, so a no-op
  edit (e.g. opening a multiselect and closing it unchanged, producing a new
  array reference) no longer writes a row update or pushes an undo entry.
  Uses JSON compare for arrays/objects, matching the existing optionsEqual
  convention; primitives keep the === fast path.

Round 3 review fixes:

- Expanded-cell popover normalizes a multiselect's initial value with
  toSelectedIds, so a single option-id string (the normal shape right after a
  select->multiselect conversion, before the row is rewritten) is no longer
  collapsed to an empty array and cleared on save.
- Column PATCH now only routes to updateColumnType on a real type change.
  updateColumnType early-returns on an unchanged type, so a payload repeating
  the current type together with new options previously applied neither; an
  unchanged type with options now routes to the options-only update. Fixed in
  both the internal and v1 column routes.

- Double-clicking a select/multiselect cell now opens the inline option
  dropdown (like date/number) instead of the fixed-height text popover, which
  rendered just a small dropdown floating in a large empty container. Removes
  the now-unreachable ExpandedSelectEditor from the expanded-cell popover.
- Options editor's add/remove controls match the sibling Filter UI: a ghost,
  muted "Add option" button with a small plus, and an X remove icon.

- Collapse `select` + `multiselect` into a single `select` column type with a
  `multiple` boolean. A cell holds one option id when single, an array when
  multiple. Validation/coercion, the contract, routes, and all cell/editor
  code now branch on `column.multiple` instead of a separate type.
- The column-config sidebar exposes an "Allow multiple" toggle (create and
  edit) and no longer offers "Unique" on select columns.
- Give the closed select cell a dropdown affordance: it renders emcn's
  `comboboxVariants` chrome (border + chevron, compacted to the row height),
  with the pills inside and the chevron flipping while the menu is open.
- Single↔multiple toggles reconcile lazily on the next row write (single
  tolerates an array by taking its first resolved option).

Drop the combobox chrome (border + chevron) from the select cell — the plain
option pills read better. Reverts the comboboxVariants barrel export too, since
nothing else uses it.

…ption

Switching a select column from multiple to single would silently keep only the
first option of any multi-valued cell. updateColumnOptions now scans the rows on
that transition and errors ("N row(s) have multiple options selected") instead
of dropping data, mirroring the type-change compatibility guard.

…elect"

…pills

When an option is deleted, cells that referenced it previously rendered a gray
fallback pill labeled with the raw internal id. They now drop the orphaned id
and fall back to empty ("None"). Editors seed their selection from the still-
valid ids too, so editing/saving such a cell writes the cleaned value.

Match the sub-block list editors (filter/sort builders): a full-width,
dashed-border ghost "Add option" button instead of a plain text button.

…opy log

- Add/update column are metadata-only server-side (row data never changes), so
  they now invalidate just the schema, not the rows. Saving a column (e.g.
  editing select options) no longer triggers a full rows refetch/flash; cells
  re-render from the refetched schema. Delete-column and workflow-group ops keep
  the rows invalidation since they do change row data.
- "Failed to copy rows" logged an empty {} for DOMExceptions; log the extracted
  message so the real reason (e.g. lost transient activation) is visible.

- Tables created before the select/multiselect merge stored `type:
  'multiselect'`, which the removed type no longer accepts — every response
  carrying such a column failed contract validation and column edits threw.
  getTableById now maps `multiselect` → `select` + `multiple: true` on read
  (covers reads, column ops via withLockedTable, and their responses); the
  migrated shape persists on the table's next schema write.
- requestJson's "Response failed contract validation" now appends a short
  "field: reason" summary of the Zod issues instead of a bare message, so the
  failing field is visible.

Only local dev tables ever held the removed `multiselect` type (the feature
never shipped), so the read-time backward-compat mapping isn't warranted.
Keeps the readable contract-validation error from the same change.

Replace the "Add option" button with a trailing empty row: the first keystroke
materializes the option and focus jumps into it (cursor at end) so typing flows
straight through. Enter in an option jumps back to the trailing row to add the
next one. Removing a row is unchanged.

CSV/JSON export serialized the raw stored value for select cells — an option
id (or an array of ids for multi) — so downloads showed opaque `opt_…` ids.
Export now resolves ids to option names: CSV comma-joins multi names; JSON
resolves values before the id→name key translation. Ids with no matching
option (deleted) are dropped.