V2 P5-backend + P7 + P8: conflict-safe sync, revocable invites, feats, multiclass, tests

P5 backend (the deferred items):
- conflict-aware cloud sync via optimistic concurrency: the server versions each
  backup blob (file mtime) and rejects a push whose base version is stale (409),
  so a second device can't silently overwrite a newer cloud copy. The client
  tracks its last-synced version; the SyncStatusIndicator surfaces a "Sync
  conflict" with one-click resolution (Use cloud / Keep this device), and the
  Settings push offers the same choice.
- revocable invites: owner can rotate a campaign's invite code (kills the old
  one) and remove a member (drops them + deletes their published characters).
  (Skipped editor/player roles — no enforcement target in the current model.)
- image storage: deliberately deferred (live images already stream de-duped on a
  separate channel; a backup blob-store is infra with no correctness gain).

P7 — subclass/feat/multiclass depth:
- feats are now first-class tracked records (name + effect text) in a Feats &
  Features sheet section, not buried in notes. Dexie v15 migration.
- 5e multiclass spell-slot calculator: a pure multiclassSlots() (full ×1, half
  ÷2, third ÷3 → full-caster table) + a sheet control to fill the slot table for
  multiclass casters. (Honest scope: tracking + slots, not per-subclass feature
  automation.)

P8 — test hardening: v2-surfaces e2e (feats, multiclass calc, signals bell,
World nav) + server tests (blob versioning, invite rotation, member removal) +
multiclass unit tests.

Gate green: 283 unit + 35 e2e + 2 realtime. App + server build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/features/characters/sheet/FeatsSection.tsx

@@ -0,0 +1,49 @@
+import { useState } from 'react';
+import { newId } from '@/lib/ids';
+import type { Feat } from '@/lib/schemas';
+import { Button } from '@/components/ui/Button';
+import { Input, Textarea } from '@/components/ui/Input';
+import { SheetSection, type SectionProps } from './common';
+
+/** Feats tracked as first-class records (name + effect) rather than buried in notes. */
+export function FeatsSection({ c, update }: SectionProps) {
+  const [name, setName] = useState('');
+
+  const add = () => {
+    if (name.trim() === '') return;
+    const feat: Feat = { id: newId(), name: name.trim(), source: '', description: '' };
+    update({ feats: [...c.feats, feat] });
+    setName('');
+  };
+  const patch = (id: string, p: Partial<Feat>) =>
+    update({ feats: c.feats.map((f) => (f.id === id ? { ...f, ...p } : f)) });
+  const remove = (id: string) => update({ feats: c.feats.filter((f) => f.id !== id) });
+
+  return (
+    <SheetSection title="Feats & Features">
+      <div className="mb-3 flex items-end gap-2">
+        <label className="flex-1 min-w-40 text-xs text-muted">
+          Add feat / feature
+          <Input value={name} onChange={(e) => setName(e.target.value)} onKeyDown={(e) => e.key === 'Enter' && add()} placeholder="Great Weapon Master, Oath of Devotion…" />
+        </label>
+        <Button variant="primary" onClick={add}>Add</Button>
+      </div>
+
+      {c.feats.length === 0 ? (
+        <p className="text-sm text-muted">No feats or features tracked yet.</p>
+      ) : (
+        <ul className="space-y-2">
+          {c.feats.map((f) => (
+            <li key={f.id} className="rounded-md border border-line bg-panel p-2">
+              <div className="flex items-center gap-2">
+                <Input className="h-8 flex-1 font-medium" value={f.name} onChange={(e) => patch(f.id, { name: e.target.value })} aria-label="Feat name" />
+                <Button size="icon" variant="ghost" className="text-danger" onClick={() => remove(f.id)} aria-label={`Remove ${f.name}`}>✕</Button>
+              </div>
+              <Textarea className="mt-1 text-xs" rows={2} value={f.description} onChange={(e) => patch(f.id, { description: e.target.value })} placeholder="What it does — kept handy at the table." aria-label={`${f.name} description`} />
+            </li>
+          ))}
+        </ul>
+      )}
+    </SheetSection>
+  );
+}