Remove chapter-level POV character

Character assignment now lives on beats only, per batch-assign. Drops
Chapter.PovCharacterId (entity, contracts, service, agent/import/MCP
tools, web UI) and the backing column via migration.

src/Novelly.Web/src/api/types.ts

@@ -173,8 +173,6 @@ export interface ChapterSummary {
   number: number
   title: string
   summary: string | null
-  povCharacterId: string | null
-  povCharacterName: string | null
   setting: string | null
   status: DraftStatus
   targetWordCount: number | null

src/Novelly.Web/src/pages/ChapterPage.tsx

@@ -84,22 +84,7 @@ export default function ChapterPage() {
           />
         </div>
 
-        <div className="mt-4 grid gap-4 sm:grid-cols-2">
-          <label className="block">
-            <span className="label">POV character</span>
-            <select
-              className="input"
-              value={chapter.povCharacterId ?? ''}
-              onChange={(e) => patch({ povCharacterId: e.target.value || null })}
-            >
-              <option value="">—</option>
-              {characters?.map((c) => (
-                <option key={c.id} value={c.id}>
-                  {c.name}
-                </option>
-              ))}
-            </select>
-          </label>
+        <div className="mt-4">
           <AutoField
             label="Setting"
             value={chapter.setting}

src/Novelly.Web/src/pages/ChaptersPage.tsx

@@ -57,7 +57,6 @@ export default function ChaptersPage() {
                   )}
                 </div>
                 <div className="flex shrink-0 items-center gap-3 text-xs muted">
-                  {chapter.povCharacterName && <span>POV: {chapter.povCharacterName}</span>}
                   <span>{chapter.beatCount} beats</span>
                   <span>{chapter.wordCount.toLocaleString()} words</span>
                   <StatusBadge status={chapter.status} />