feat(concurrency): configurable cooldown + adaptive-headroom auto-reduce banner

Consumes the backend's concurrency-fixes (commit 2d27666) — additive to
[email protected], NO version bump. ConcurrencyStatusEntry gains
cooldownMs / autoReduced / autoReducedFrom? / notice?; new
ConcurrencyCooldownResponse / SetConcurrencyCooldownRequest + GET/PUT
/concurrency/cooldown/:providerId.

FE:
- Pure core (logic/view-model.ts): DEFAULT_COOLDOWN_MS; parseCooldownInput
  (non-negative int — 0 is valid, unlike the limit); normalizeCooldown;
  cooldownLabel ("350ms"/"1.2s"/"0ms (off)"); viewConcurrencyStatus extended
  (cooldown + autoReduce fields; auto-reduce → warning badge, not busy);
  viewAutoReduce/autoReduceNotices (banner view — prefers backend notice,
  synthesizes a fallback); summarizeStatus "N auto-reduced" fragment;
  normalizeConcurrencyStatus coerces new fields (immutable readonly build;
  autoReducedFrom/notice only when autoReduced===true); normalizeConcurrencyCooldown.
- Types (logic/types.ts): re-export the 2 new contract types +
  ConcurrencyCooldownResult + Get/SaveConcurrencyCooldown ports.
- UI: ConcurrencyCooldownRow.svelte (inline-edit cooldown + Save → PUT, seeded
  via the ChatLimitField pattern); AutoReduceBanner.svelte (dismissible banner —
  backend notice + "Was N, now M." + "Restore to N"); ConcurrencyView renders
  the cooldown per status card + the banner section. The banner persists while
  autoReduced===true, is dismissible, and clears automatically once a poll shows
  autoReduced===false after a restore PUT.
- Store (store.svelte.ts): getConcurrencyCooldown + setConcurrencyCooldown
  (surface 400/404/503 as ok:false; normalize at the seam) + interface decls.
- App.svelte: saveConcurrencyCooldown adapter → ConcurrencyView.
- Tests: +47 (view-model cooldown/auto-reduce/normalizers; component banner
  render, cooldown PUT, restore clears banner, dismiss; store cooldown GET/PUT).

Re-synced the file: dep (bun install) + re-mirrored .dispatch/transport-contract.
reference.md. typecheck 0/0, 1048 tests green (run twice), biome clean, build OK.

Worktree env: an untracked dispatch-backend → backend symlink was created in the
worktree parent so the canonical file:../dispatch-backend/... paths resolve
(NOT committed — per the §2d/§2j worktree convention).

1 files changed, 21 insertions, 2 deletions

diff --git a/src/features/concurrency/index.ts b/src/features/concurrency/index.ts
index 151acb8..95eb5ed 100644
--- a/src/features/concurrency/index.ts
+++ b/src/features/concurrency/index.ts
@@ -1,7 +1,9 @@
 export type {
+  // Contract shapes re-exported for a single import surface.
+  ConcurrencyCooldownResponse,
+  ConcurrencyCooldownResult,
   ConcurrencyDeleteResult,
   ConcurrencyLimitEntry,
-  // Contract shapes re-exported for a single import surface.
   ConcurrencyLimitResponse,
   ConcurrencyLimitResult,
   ConcurrencyLimitsResponse,
@@ -10,30 +12,47 @@ export type {
   ConcurrencyStatusResponse,
   ConcurrencyStatusResult,
   DeleteConcurrencyLimit,
+  GetConcurrencyCooldown,
   GetConcurrencyLimit,
   LoadConcurrencyLimits,
   LoadConcurrencyStatus,
+  RestoreOutcome,
+  SaveConcurrencyCooldown,
   SaveConcurrencyLimit,
+  SetConcurrencyCooldownRequest,
   SetConcurrencyLimitRequest,
 } from "./logic/types";
-export type { Badge, ConcurrencyLimitView, ConcurrencyStatusView } from "./logic/view-model";
+export type {
+  AutoReduceNotice,
+  Badge,
+  ConcurrencyLimitView,
+  ConcurrencyStatusView,
+} from "./logic/view-model";
 export {
+  autoReduceNotices,
+  cooldownLabel,
+  DEFAULT_COOLDOWN_MS,
   formatPauseDuration,
+  normalizeConcurrencyCooldown,
   normalizeConcurrencyLimit,
   normalizeConcurrencyLimits,
   normalizeConcurrencyStatus,
   normalizeLimit,
+  parseCooldownInput,
   parseLimitInput,
   pauseLabel,
   providerFromModel,
   providerOptions,
   summarizeLimits,
   summarizeStatus,
+  viewAutoReduce,
   viewConcurrencyLimit,
   viewConcurrencyLimits,
   viewConcurrencyStatus,
   viewConcurrencyStatuses,
 } from "./logic/view-model";
+export { default as AutoReduceBanner } from "./ui/AutoReduceBanner.svelte";
+export { default as ConcurrencyCooldownRow } from "./ui/ConcurrencyCooldownRow.svelte";
 export { default as ConcurrencyLimitRow } from "./ui/ConcurrencyLimitRow.svelte";
 export { default as ConcurrencyView } from "./ui/ConcurrencyView.svelte";