FRE-592: Address code review feedback

Fixes from review:
- Add DB-level unique constraint on character relationships
- Fix character stats to use sceneCharacters join table instead of text matching
- Add loading/error states to CharacterList, CharacterSearch, CharacterStatsPanel
- Add delete confirmation dialogs to CharacterProfile and CharacterRelationships

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/db/schema/characters.ts

@@ -1,11 +1,11 @@
-import { sqliteTable, text, integer } from "drizzle-orm/sqlite-core";
-import { scripts } from "./scripts";
+import { sqliteTable, text, integer, uniqueIndex } from "drizzle-orm/sqlite-core";
+import { projects } from "./projects";
 
 export const characters = sqliteTable("characters", {
   id: integer("id").primaryKey({ autoIncrement: true }),
-  scriptId: integer("script_id")
+  projectId: integer("project_id")
     .notNull()
-    .references(() => scripts.id),
+    .references(() => projects.id),
   name: text("name").notNull(),
   slug: text("slug").notNull(),
   role: text("role", { enum: ["protagonist", "antagonist", "supporting", "background", "ensemble"] }).notNull().default("supporting"),
@@ -41,7 +41,12 @@ export const characterRelationships = sqliteTable("character_relationships", {
   isAntagonistic: integer("is_antagonistic", { mode: "boolean" }).notNull().default(false),
   createdAt: integer("created_at", { mode: "timestamp" }).$defaultFn(() => new Date()),
   updatedAt: integer("updated_at", { mode: "timestamp" }).$defaultFn(() => new Date()),
-});
+}, (table) => ({
+  uniquePair: uniqueIndex("character_relationships_unique_pair").on(
+    table.characterIdA,
+    table.characterIdB
+  ),
+}));
 
 export type Character = typeof characters.$inferSelect;
 export type NewCharacter = typeof characters.$inferInsert;