fix(workflows): keep history loading off dashboard animation ticks

[tt-a1i]

Problem

Opening the Workflow dashboard can block keyboard input for seconds. Its 120 ms animation timer synchronously scans and hydrates all historical runs before filtering for the current request. Fixes #420.

Value

Keep dashboard animation and navigation responsive as workflow history accumulates, while preserving live progress, canonical settlement and historical transcript/report access.

Approach

• Read the historical overview once per dashboard instance and filter raw metadata before normalizing unrelated records.
• Reconcile live in-memory entries on subsequent frames; read a newly settled run once from canonical persistence, with retained projections as the fallback.
• Hydrate side artifacts only on transcript navigation or report export, and reuse them for rendering.
• Preserve the investigation and evidence limits in docs/research/WORKFLOW_DASHBOARD_REFRESH_2026-09-07.md.

Validation

• Regression tests failed on the baseline: ten animation ticks plus return navigation caused 11 history reads; opening the overview caused two artifact reads. Both are zero after the fix.
• Dashboard tests: 27 passed, including lazy transcript rendering, terminal transition and retained-run discovery.
• GitHub CI: all required checks passed (Node 22.19.0, Node 24, Background terminals / Windows).
• bun run check: passed.
• bun run test: Node 1430 passed / 1 skipped; Vitest 30 passed.
• Read-only local loader probe returned zero entries: baseline Node 3522/3327/3952 ms; fixed 798/3/3 ms. These are exploratory measurements under concurrent load and cache effects, not a controlled speedup claim.
• Real terminal acceptance after reloading the fixed package has not been performed. The existing running user's session was preserved.

Impact

• User-visible: stable animation/navigation no longer rescans history; historical detail loads on demand.
• Model-visible tools/context: none.
• Runtime/lifecycle: dashboard projections only; execution authority, cancellation and persistence contracts are unchanged.
• Persisted configuration/data: no format changes or migrations.
• Compatibility/risk: external historical edits appear after reopening the dashboard; first metadata discovery and first transcript opening still perform synchronous reads. Separate ordinary conversation-view lag is outside this reproduced path.