fix(frontend): remove duplicated streams/streams/[streamId] route and add redirect

[omoh5]

Summary

Fixes #1084 — removes the dead /streams/streams/[streamId] route that was a leftover from a previous refactor, and adds a permanent redirect to the canonical /streams/:id route.

Problem

• frontend/src/app/streams/streams/[streamId]/page.tsx was a duplicated dynamic route alongside frontend/src/app/streams/[id]/page.tsx
• The code-searcher confirmed zero references to the streams/streams/ path anywhere in the codebase
• With two competing dynamic routes, Next.js can route to either one, causing confusion for navigation and SEO (duplicate content at two URLs)

Changes

🔴 Removed

• frontend/src/app/streams/streams/[streamId]/page.tsx (343 lines deleted)
  • Confirmed dead code — no imports, links, or navigation references point to it
  • All links in the codebase use /streams/<id> which resolves to the [id] route

🟢 Added

• frontend/next.config.ts — permanent redirect (HTTP 308)
  • /streams/streams/:streamId → /streams/:streamId
  • Ensures any external links or bookmarks to the old path seamlessly land on the correct page

Verification

• npx tsc --noEmit — no new errors (pre-existing errors in useIncomingStreams.test.ts are unrelated)
• Pre-commit lint hook passed
• Code reviewer confirmed no issues
• Directory confirmed removed

Out of scope

• Restructuring the whole streams route tree
• Changing the stream detail UI