feat(security): safeFetch wrapper with manual redirect and timeout defaults

Closes issue 218. Flips the convention from "remember to opt in to
redirect: manual" to "remember to opt out". Every outbound fetch that
doesn't pin a hard-coded host now routes through safeFetch and inherits
AbortSignal.timeout(15_000) so a tar-pit upstream can no longer pin a
worker indefinitely. The local AI client also gates on
requirePublicHost: true since its host is user-supplied; operators
running self-hosted Ollama / LM Studio on an RFC1918 address keep their
escape hatch via ALLOW_LOCAL_AI_PRIVATE_HOSTS=true (also enforced at
write-time in /api/user/ai-provider).

14 outbound call sites migrated. The four that already pinned manual
redirect (the historic templates) keep their semantics; the wrapper
preserves an explicit init.redirect. Adds undici as an explicit
dependency so the connect-time pin landing alongside this can rely on
the documented API rather than a transitive hop.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/bugreport/route.ts

@@ -11,6 +11,7 @@ import { checkRateLimit } from "@/lib/rate-limit";
 import { auditLog } from "@/lib/auth/audit";
 import { prisma } from "@/lib/db";
 import { decrypt } from "@/lib/crypto";
+import { safeFetch } from "@/lib/safe-fetch";
 import { NextRequest } from "next/server";
 import { z } from "zod/v4";
 
@@ -120,7 +121,7 @@ export const POST = apiHandler(async (request: NextRequest) => {
   }
 
   // Create the issue
-  const issueRes = await fetch(
+  const issueRes = await safeFetch(
     `https://api.github.com/repos/${ghRepo}/issues`,
     {
       method: "POST",