feat: Engine durability hardening + dashboard redesign

[kasvith]

Summary

Two bodies of work on this branch: hardening the durable execution engine
for correctness under concurrency, and a ground-up visual redesign of the
dashboard around a single design direction. Grouped into 14 dependency-ordered
commits so the history reads as a progression (shared primitives land before the
surfaces that consume them; tests and rebuilt assets come last).

Engine — durability & correctness

• Lock fencing + ownership guards on job claim so a recovered/stale worker
  can't resume a job that's since been re-claimed (FOR UPDATE SKIP LOCKED
  plus a fence token).
• Durable retries with backoff and a per-step :timeout.
• Child-workflow linkage — parallel children and call_workflow /
  start_workflow sub-workflows are linked to their parent execution.
• Sleep/wait correctness — a dedicated sleep waker; :waiting suspension
  markers no longer drift the live window.
• Tests de-mocked — real Postgres-backed suites for parallel race, retries,
  the query API, timeout-worker integration, and a concurrency integration test.

⚠️ Requires migrations. Two new engine migrations ship here
(v20260623000000_add_lock_fencing, v20260623000001_add_child_workflow_link).
Run Durable.Migration.up() (the demo's upgrade migration is included as an
example).

Dashboard — redesign

One direction runs through every surface: an instrument panel for durable
execution. The indigo accent now carries a single meaning — now / live / you
are here (active nav, running graph edge, in-flight timeline bars). Machine
facts render in mono, human prose in Inter. Status is the only decorative color.

• Shell — sidebar grouped into Observe / Operate with the live-rail
  active marker and the pulse brand mark (a muted oscilloscope baseline + one
  indigo heartbeat beat — the worker heartbeat made literal); topbar command
  toolbar (⌘K trigger · version · GitHub · theme).
• Shared primitives — label / field / field_list, local_time plus a
  future-aware relative_time with JS-localized tooltips, a JSON highlighter,
  DataTable label-idiom headers, and the shared LogLine / StepDetail
  components reused across tabs and the flow inspector.
• Workflow flow-graph island — ReactFlow nodes (step, start, end, gateway,
  child-workflow) + animated status edge, dagre layout, runtime status overlay.
• Detail tabs — Summary, Logs, Timeline (absolute-time Gantt with a frozen
  gutter), History (vertical trace spine), I/O.
• List / overview pages — a segmented status-readout cluster on Overview
  and the Workflows cards, the executions list on DataTable, Settings field-list.
• Design decisions codified in durable_dashboard/DESIGN.md (direction,
  live-rail signature, status-readout pattern).

Follow-up polish (a1b2590)

A pass over the chrome and the step inspector after using it on real data:

• ⌘K palette is now live. It had shipped unmounted (the trigger dispatched
  to nothing), so it's wired into the app shell and rewritten to search the
  console's nouns, grouped — Go to (pages, incl. the previously-missing
  Executions), Workflows (live list_workflows), Recent runs (latest
  executions). Live data is snapshotted on open, filtered in-memory per keystroke;
  the selected row carries the live rail + a ↵ hint.
• Topbar command toolbar — compact ⌘K trigger (width hugs content, no dead
  middle gap, single ⌘K chip), a hairline divider, then running version ·
  GitHub link · theme toggle as ghost icon controls (github brand icon
  added to Core.icon).
• Pulse brand mark — replaces the tinted "monitor tile + dot"; indigo stays
  earned by the live signal rather than spent on a branded surface.
• Step inspector — widened the shared StepDetail panel cap
  (max-w-4xl → max-w-5xl); I/O JSON boxes now fill their column and the grid
  collapses to one full-width column when only one side has data, so a cron
  step's output isn't penned into a half-panel beside an empty "No input" cell.

Copy, full-width inspector, faceted filters (9341826, c2be144)

• Copy to clipboard — a Core.copy_button primitive (one delegated
  listener, no per-button hook) baked into every JSON block plus opt-in on the
  execution id and Settings config values.
• Step inspector now fills its container (cap removed); plain-text log
  messages render in a framed code block instead of bare text.
• Faceted Executions filter bar — replaces the (exact-match!) free-text
  search with a query-builder: workflow combobox (autocomplete from known
  names), multi-select status, relative/custom time range, and an execution-id
  prefix filter with jump-on-full-uuid. URL-param driven, so filtered views are
  shareable. Backed by new Query.apply_filters clauses (:id, :id_prefix,
  multi :status) with tests.
• READMEs refreshed for the current dashboard IA and features.

Testing

• Dashboard: 114 tests green; covers core primitives (incl. local_time /
  future relative_time), DataTable, LogLine, Timeline, flow graph, tabs, routes,
  the command palette, and the faceted ExecutionFilters bar.
• Engine: compiles --warnings-as-errors; new DB-backed concurrency / retry /
  race / query suites (need Postgres on the test port), incl. the new
  id / id-prefix / status-list / time filter clauses.

Reviewing

Commit-by-commit is the intended path. Engine (6b56c35, 53f7ea5) is
independent of the dashboard. Within the dashboard, c433ebb (shared
primitives) is the foundation the rest build on; a1b2590 is the latest
chrome/inspector polish.

Note: bundled assets (priv/static) are committed alongside the changes that
need them; the .claude/settings.json toggle is 4013a84.