feat(db): enforce globally unique issue prefixes and identifiers

Derive issue_prefix from first 3 letters of company name with
deterministic suffixes on collision. Migration rebuilds existing
prefixes, reassigns issue numbers, and adds unique indexes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/services/companies.ts

@@ -1,4 +1,4 @@
-import { eq, sql, count } from "drizzle-orm";
+import { eq, count } from "drizzle-orm";
 import type { Db } from "@paperclip/db";
 import {
   companies,
@@ -25,6 +25,50 @@ import {
 } from "@paperclip/db";
 
 export function companyService(db: Db) {
+  const ISSUE_PREFIX_FALLBACK = "CMP";
+
+  function deriveIssuePrefixBase(name: string) {
+    const normalized = name.toUpperCase().replace(/[^A-Z]/g, "");
+    return normalized.slice(0, 3) || ISSUE_PREFIX_FALLBACK;
+  }
+
+  function suffixForAttempt(attempt: number) {
+    if (attempt <= 1) return "";
+    return "A".repeat(attempt - 1);
+  }
+
+  function isIssuePrefixConflict(error: unknown) {
+    const constraint = typeof error === "object" && error !== null && "constraint" in error
+      ? (error as { constraint?: string }).constraint
+      : typeof error === "object" && error !== null && "constraint_name" in error
+        ? (error as { constraint_name?: string }).constraint_name
+        : undefined;
+    return typeof error === "object"
+      && error !== null
+      && "code" in error
+      && (error as { code?: string }).code === "23505"
+      && constraint === "companies_issue_prefix_idx";
+  }
+
+  async function createCompanyWithUniquePrefix(data: typeof companies.$inferInsert) {
+    const base = deriveIssuePrefixBase(data.name);
+    let suffix = 1;
+    while (suffix < 10000) {
+      const candidate = `${base}${suffixForAttempt(suffix)}`;
+      try {
+        const rows = await db
+          .insert(companies)
+          .values({ ...data, issuePrefix: candidate })
+          .returning();
+        return rows[0];
+      } catch (error) {
+        if (!isIssuePrefixConflict(error)) throw error;
+      }
+      suffix += 1;
+    }
+    throw new Error("Unable to allocate unique issue prefix");
+  }
+
   return {
     list: () => db.select().from(companies),
 
@@ -35,12 +79,7 @@ export function companyService(db: Db) {
         .where(eq(companies.id, id))
         .then((rows) => rows[0] ?? null),
 
-    create: (data: typeof companies.$inferInsert) =>
-      db
-        .insert(companies)
-        .values(data)
-        .returning()
-        .then((rows) => rows[0]),
+    create: async (data: typeof companies.$inferInsert) => createCompanyWithUniquePrefix(data),
 
     update: (id: string, data: Partial<typeof companies.$inferInsert>) =>
       db