Remove obsolete variable runtime seams left after #447 phase 1

[BorisTyshkevich]

Found while shipping #447 phase 1. Removing the curated-filter model left several exported fields and methods with no production consumer. This issue removes only seams that remain obsolete after #447 phase 2 settles the variable runtime.

Candidate removals

• FilterBarHandle.updateStatus
• FieldStatus
• the no-op updateStatus implementation in src/ui/time-range-field.ts
• ViewerFilterState.options when no production path populates it
• ViewerFilterState.optionsRev when no production path advances it
• any exported function, field or adapter seam whose only caller belonged to the removed curated-filter implementation

FilterBarHandle.updateStatus and FieldStatus currently remain covered only by the filter-bar routing test. A direct-input variable has no transient status, and ui/dashboard.ts no longer calls the method.

ViewerFilterState.options is currently always null and optionsRev is always 0, but #447 phase 2 may populate them from the batched option query. Audit them after phase 2 rather than deleting and immediately restoring them.

Compatibility boundaries

Do not remove legacy schemas or generated types merely because they describe curated filters. dashboard-v1.schema.json, the corresponding definitions in library-v2.bundle.schema.json, and DashboardFilterDefinitionV1 remain load-bearing while stored-workspace v2/v3/v4 and portable-bundle-v1 records are supported.

This issue is dead-code removal only. It must not alter persisted data, interchange compatibility or Dashboard behaviour.

Acceptance

• No exported function, method or field exists solely because a deleted caller used to consume it.
• Candidate fields needed by Replace curated Dashboard filters with inferred Variables and batched option queries #447 phase 2 are retained and have real production consumers.
• Legacy read support remains intact.
• No behaviour changes.
• npm test, npm run check:arch, and npm run test:e2e on Chromium and WebKit stay green.

Split from #457. Related issues: #457 and #459.

[BorisTyshkevich]

Ship log — #460

Single-phase issue (no ## Phases checklist, no ### Phase N headings).
One branch off main, one PR.

Phase	Status	PR
— whole issue	in review	#480

Handoff

Landed — branch refactor/dead-filter-seams-460, 1 commit.

The issue was filed before #447 phase 2, #457 and #459 landed, so its
candidate list needed re-auditing against the current tree rather than
applied as originally written:

• FilterBarHandle.updateStatus / FieldStatus / the no-op in
  time-range-field.ts: still dead, removed. Confirmed by grep across
  src/ and tests/: zero production callers anywhere (not even
  dashboard.ts, whose own doc comment claiming it "still publishes a status
  map per wave" was itself stale — deleted with the rest). Three no-op
  implementations came out with it: the multi-select field, the
  option-backed select, and the time-range control's own no-op.
• ViewerFilterState.options/optionsRev (now ViewerVariableState,
  renamed by Rename surviving filter terminology to Dashboard variables #459): audited and KEPT, per the issue's own instruction.
  Phase 2 gave them a real producer — applyOptions in
  dashboard-viewer-session.ts mutates both, and dashboard.ts reads them
  through currentVariableBar?.setVariableOptions(states). Deleting them
  would have been deleting live code.
• Broader sweep of every other export in the ten filter/variable-adjacent
  modules named in the issue's own "any exported function/field/adapter
  seam…" bullet turned up nothing else — every other export with no
  external caller is an ordinary internal helper type/constant used only
  within its own declaring file (normal under this repo's 100%-coverage
  convention), not migration debris.
• Legacy schemas/types (dashboard-v1.schema.json, the corresponding
  library-v2.bundle.schema.json definitions, DashboardFilterDefinitionV1)
  were confirmed untouched — out of scope per the issue.

One review finding, fixed in the same commit: a doc comment at
variable-bar.ts (time-range handle registration) still read "status/
dispose/focus/refresh folds" after the status fold was deleted — corrected
to "dispose/focus/refresh folds".

Deferred acceptance criteria: none. All 4 global bullets claimed.

Follow-ups filed: none — nothing new turned up beyond the issue's own
named candidates.

Reconciled: CHANGELOG [Unreleased] (new ### Removed entry). No ADR
addendum needed (ADR-0003 never mentioned this seam). Not referenced by
roadmap #68 — a small split-off cleanup issue, not a tracked phase.

Gate: 174 test files / 5601 tests, per-file coverage met (100/100/100/100
on both edited files), tsc --noEmit / check:arch / check:schemas clean,
build 1,819,439 bytes. e2e 244 passed on chromium + webkit (Firefox comes
from CI in this sandbox — unshare CLONE_NEWPID EPERM).