Fix Cloud tenant issue identifier routes (#5196)

## Summary

- Allow Cloud tenant issue identifiers with alphanumeric prefixes, such
as `PC1897-1`, to normalize as issue references.
- Resolve those identifiers through issue detail/update routes, active
run/live run polling, activity, costs, and `issueService.getById`.
- Keep UI issue-link parsing aligned so tenant links normalize back to
`/issues/<IDENTIFIER>`.

## Root Cause

Cloud tenant issue prefixes include digits from the stack-id hash. The
app-side route normalization still accepted only all-letter prefixes, so
`/api/issues/PC1897-1` skipped identifier lookup and fell through as a
non-UUID id.

## Verification

- `pnpm exec vitest run packages/shared/src/issue-references.test.ts
ui/src/lib/issue-reference.test.ts
server/src/__tests__/issue-identifier-routes.test.ts
server/src/__tests__/activity-routes.test.ts
server/src/__tests__/costs-service.test.ts
server/src/__tests__/agent-live-run-routes.test.ts
server/src/__tests__/issues-service.test.ts`
- `pnpm --filter @paperclipai/shared typecheck && pnpm --filter
@paperclipai/server typecheck`
- `git diff --check`

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/routes/activity.ts

@@ -1,6 +1,7 @@
 import { Router } from "express";
 import { z } from "zod";
 import type { Db } from "@paperclipai/db";
+import { normalizeIssueIdentifier } from "@paperclipai/shared";
 import { validate } from "../middleware/validate.js";
 import { activityService, normalizeActivityLimit } from "../services/activity.js";
 import { assertAuthenticated, assertBoard, assertCompanyAccess } from "./authz.js";
@@ -24,8 +25,9 @@ export function activityRoutes(db: Db) {
   const issueSvc = issueService(db);
 
   async function resolveIssueByRef(rawId: string) {
-    if (/^[A-Z]+-\d+$/i.test(rawId)) {
-      return issueSvc.getByIdentifier(rawId);
+    const identifier = normalizeIssueIdentifier(rawId);
+    if (identifier) {
+      return issueSvc.getByIdentifier(identifier);
     }
     return issueSvc.getById(rawId);
   }