chore(deps): drop Grpc.AspNetCore — use Google.Protobuf for ProtoBuf-only storage

[kirill-abblix]

Summary

• Abblix.Oidc.Server uses ProtoBuf only for Redis storage (Features/Storages/Proto/*.proto with GrpcServices="None") and never hosts gRPC endpoints — AddGrpc / MapGrpcService / Grpc.AspNetCore.Server are not present in the codebase.
• The Grpc.AspNetCore umbrella is replaced with the runtime-only Google.Protobuf 3.34.1 (matches the Abblix.Utils version). Grpc.Tools 2.78.0 stays as the build-time driver for protoc / MSBuild.
• Aligns with the canonical pattern in Docs/wiki/protobuf-redis-session-storage.md § MSBuild integration (updated today).
• All <Protobuf> includes already had GrpcServices="None" — no further change needed.

Cross-repo: parallel PRs Abblix/AuthenticationService#80 and Abblix/Kezio#161 apply the same approach.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[kirill-abblix]

Post-merge note (2026-04-29): rolled back from master.

This PR was created against master by mistake — it should have targeted develop, like every other feature/refactor PR in this repo. After merge I caught the Git Flow violation and reset master to the pre-session tip (71dd981) via git push --force-with-lease.

The change itself (Grpc.AspNetCore → Google.Protobuf in Abblix.Oidc.Server.csproj) survives on develop through the master → develop back-merge in e7b9d65. It will re-land on master through the next release branch, the way the repo's Git Flow expects.

Net state:

• master tip: 71dd981 (pre-chore(deps): drop Grpc.AspNetCore — use Google.Protobuf for ProtoBuf-only storage #68, has Grpc.AspNetCore again).
• develop tip: e7b9d65 (has Google.Protobuf from this PR via the merge).
• This PR remains MERGED in GitHub metadata because the API blocks changing base of a closed PR; the comment is the only way to annotate the audit trail.

Codified feature → develop rule in this repo's CLAUDE.md and in cross-repo memory (feedback-default-base-branch-develop.md) so the same drift doesn't recur.