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.