Fixes batch 1: modal focus, campaign system, combat difficulty, origin desc

- Modal: focus into the dialog ONCE on open (not on every parent re-render), and
  prefer the first field over the X button — fixes focus jumping to the close
  button on each keystroke in the handout composer (and every other composer).
- Campaign edit: hide the System selector entirely (it's fixed after creation).
- Combat difficulty: rate against the PCs actually in the encounter (falls back to
  the roster) so adding a player updates the reading.
- Character builder: ancestry/background description is now a scrollable panel
  instead of clamped to 3 lines (no longer cut off on small screens).

223 unit + key e2e green.

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

src/features/campaigns/CampaignsPage.tsx

@@ -258,19 +258,18 @@ function CampaignFormModal({ campaign, onClose }: { campaign?: Campaign; onClose
             placeholder="Curse of Strahd"
           />
         </Field>
-        <Field label="System">
-          <Select
-            value={system}
-            disabled={!!campaign}
-            onChange={(e) => setSystem(e.target.value as typeof system)}
-          >
-            {SYSTEM_OPTIONS.map((o) => (
-              <option key={o.id} value={o.id}>
-                {o.label}
-              </option>
-            ))}
-          </Select>
-        </Field>
+        {/* System is fixed once a campaign exists (content + characters depend on it). */}
+        {!campaign && (
+          <Field label="System">
+            <Select value={system} onChange={(e) => setSystem(e.target.value as typeof system)}>
+              {SYSTEM_OPTIONS.map((o) => (
+                <option key={o.id} value={o.id}>
+                  {o.label}
+                </option>
+              ))}
+            </Select>
+          </Field>
+        )}
         <Field label="Description">
           <Textarea
             value={description}

src/features/characters/builder/CreationWizard.tsx

@@ -378,7 +378,7 @@ function OriginPicker({ title, options, value, onPick }: { title: string; option
         ))}
         {options.length === 0 && <p className="text-xs text-muted">Loading…</p>}
       </div>
-      {sel?.desc && <p className="mt-1 line-clamp-3 text-xs text-muted">{sel.desc}</p>}
+      {sel?.desc && <p className="mt-1 max-h-32 overflow-y-auto whitespace-pre-wrap rounded-md border border-line bg-surface-2 p-2 text-xs text-muted">{sel.desc}</p>}
     </div>
   );
 }

src/features/combat/EncounterTracker.tsx

@@ -71,7 +71,10 @@ export function EncounterTracker({ encounter, campaign }: { encounter: Encounter
   // Difficulty budget from monster combatants vs the campaign's PCs. Once combat
   // has started, rate against the levels captured at that time (snapshot) so the
   // reading — and the assistant's history — reflects the party as it was.
-  const currentLevels = characters.filter((c) => c.kind === 'pc').map((c) => c.level);
+  // Rate against the PCs actually IN the fight (so adding a player updates the
+  // difficulty); fall back to the campaign roster before any PC is added.
+  const encounterPcLevels = encounter.combatants.filter((c) => c.kind === 'pc' && c.level !== undefined).map((c) => c.level as number);
+  const currentLevels = encounterPcLevels.length > 0 ? encounterPcLevels : characters.filter((c) => c.kind === 'pc').map((c) => c.level);
   const partyLevels = encounter.partyLevelsSnapshot?.length ? encounter.partyLevelsSnapshot : currentLevels;
   const monsters = encounter.combatants
     .filter((c) => c.kind === 'monster')