fix(gateway): map /api/notifications to the notification controller path

[devin-ai-integration]

Summary

/api/notifications returned 404 through the gateway: the route strips its own prefix, but NotificationController is [Route("api/[controller]")] — singular — so the forwarded path (/) matched nothing. Re-prefixing after the strip makes the fifth service reachable like the other four.

 "Match": { "Path": "/api/notifications/{**catch-all}" },
-"Transforms": [{ "PathRemovePrefix": "/api/notifications" }]
+"Transforms": [
+  { "PathRemovePrefix": "/api/notifications" },
+  { "PathPrefix": "/api/notification" }
+]

Pre-existing bug, unrelated to the four extraction PRs; kept in its own PR because src/ApiGateway/** is off-limits to those branches.

Verified on a local integration branch (main + #88 + #89 + #90 + #91) with the full compose stack up: curl :5000/api/notifications → 200 with the persisted notification rows, and the other four routes unaffected.

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/25839f55096f4d6187d729c0a19f29f9
Open in Devin Desktop: https://partner-workshops.devinenterprise.com/desktop/session/25839f55096f4d6187d729c0a19f29f9?variant=devin
Requested by: @DhrovS

[devin-ai-integration]

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