fix(translate): replace fromStore+ with +subscribe to prevent reactive loop, add runComplete flag, show error_message, collapsible run results

- TranslationRunGlobalIndicator: replace fromStore + 6x  with
  (() => store.subscribe()) to prevent accumulating render_effect
  instances via createSubscriber that caused infinite Svelte reactive flush
- translate/[id]/+page.svelte: add runComplete flag to hide progress bar
  after completion without touching the store; add collapsible run detail
  cards with status badge, counts, and error_message; filter invalid runs
- translationRun.js: remove stale guard (no longer needed)
- Sidebar.svelte: fix mobile overlay close on route change
- docs/adr/ADR-0007-rejected-fromStore-derived.md: document REJECTED pattern

docs/adr/ADR-0007-rejected-fromStore-derived.md

@@ -0,0 +1,61 @@
+# ADR-0007: REJECTED — `fromStore` + multiple `$derived` in Svelte 5
+
+## Status
+REJECTED — pattern forbidden in ss-tools frontend.
+
+## Context
+`fromStore(store)` returns a reactive object whose `.current` property
+reflects the underlying Svelte writable store. Using it with multiple
+`$derived(runState.current?.xxx)` values creates persistent `render_effect`
+instances via Svelte's `createSubscriber` on every reactive re-evaluation.
+
+### Observed failure (ss-tools, May 2026)
+`TranslationRunGlobalIndicator` used 6 `$derived` reading `runState.current`.
+Each `$derived` re-evaluation (triggered by store update) called `subscribe()`
+which called `render_effect()` inside `createSubscriber`. The `render_effect`
+teardown queues a microtask that decrements the subscriber count. When all
+teardowns execute, subscriber count drops to zero, which triggers `increment(version)`,
+which marks all `$derived` as dirty again — creating an **infinite reactive flush loop**.
+
+### Symptoms
+- After ~300 store poll cycles, the browser tab reaches 100% CPU on 2 cores.
+- Svelte runtime (`flush` → `Ve` → `yn` → `fn`) throws `Uncaught` repeatedly.
+- `CTFFznDe.js` chunk enters infinite loop.
+- Page becomes completely unresponsive.
+
+## Decision
+`fromStore` MUST NOT be used with `$derived` when the `.current` object is
+read by more than one `$derived` in the same component.
+
+Use `$effect(() => store.subscribe(s => state = s))` instead — this creates
+exactly ONE subscription per component lifecycle, with no accumulating
+`render_effect` instances.
+
+## Consequences
+### Positive
+- Store subscription is created once per component mount and cleaned up on destroy.
+- No accumulating `render_effect` instances → no infinite reactive loop.
+- Works correctly in Svelte 5.43.x.
+
+### Negative
+- Requires explicit `$state` initial value and `$effect` subscription.
+- Slightly more verbose than `fromStore`.
+
+## Migration
+Replace:
+```javascript
+const state = fromStore(store);
+let foo = $derived(state.current?.foo || null);
+let bar = $derived(state.current?.bar || 0);
+```
+
+With:
+```javascript
+let _state = $state(initialValue);
+$effect(() => {
+    const unsub = store.subscribe(s => { _state = s; });
+    return () => unsub();
+});
+let foo = $derived(_state?.foo || null);
+let bar = $derived(_state?.bar || 0);
+```