feat(storage_challenge): add LEP-6 compound storage challenge runtime

[j-rafique]

Implements the PR3 compound storage challenge runtime on top of the updated LEP-6 PR1/PR2 foundation.

Highlights:

• Add compound proof request/response fields and regenerated supernode proto bindings.
• Add recipient-side GetCompoundProof handler with signed responses and range validation.
• Add challenger-side LEP6Dispatcher for assigned-target dispatch across RECENT/OLD buckets.
• Add result buffer implementing host_reporter ProofResultProvider with chain cap throttling.
• Add deterministic cascade metadata resolution helpers for artifact count, key, and exact artifact size.
• Add production ChainTicketProvider backed by final Lumera x/action ListActionsBySuperNode query.
• Wire startup to use ChainTicketProvider and cascade metadata/action size resolution instead of NoTicketProvider.
• Classify target RPC timeout/no-response as TIMEOUT_OR_NO_RESPONSE and malformed transcripts as INVALID_TRANSCRIPT.
• Extend action module bindings/mocks with ListActionsBySuperNode.

Lumera dependency/source:

• github.com/LumeraProtocol/lumera v1.12.0-rc.0.20260430142036-451f8a8e7ff3
• chain source: lumera/master 451f8a8e7ff30b3370cba59fab8e6228473a348b

Validation:

• git diff --check origin/supernode/LEP-6-deterministic-primitives..HEAD: pass
• go test ./pkg/lumera/... ./pkg/storagechallenge/... ./supernode/storage_challenge ./supernode/transport/grpc/storage_challenge ./supernode/cmd ./supernode/host_reporter: pass
• go vet ./pkg/lumera/... ./pkg/storagechallenge/... ./supernode/storage_challenge ./supernode/transport/grpc/storage_challenge ./supernode/cmd ./supernode/host_reporter: pass
• go test ./...: fails only at pre-existing local libwebp headers in pkg/storage/files (webp/decode.h, webp/encode.h missing); PR3-focused packages pass.

Plan: docs/plans/LEP6_SUPERNODE_IMPLEMENTATION_PLAN_v3_MASTER.md PR3

[roomote-v0]

Rooviewer   See task

Re-reviewed at 5a99549. All four issues from previous reviews are now fixed. No new issues found.

• Race condition in ensureClient() -- secureSupernodeClientFactory.ensureClient() reads/writes grpcClient without synchronization; concurrent Dial() calls will race (lep6_client_factory.go)
• Transcript hash divergence between challenger and recipient -- Recipient computes TranscriptHash with empty DerivationInputHash while challenger uses the actual value, producing different hashes for the same proof (handler.go)
• classifyProofFailure misclassifies non-timeout RPC errors as HASH_MISMATCH -- Infrastructure errors (PermissionDenied, Internal, etc.) are reported as hash mismatches rather than transcript/connectivity failures (lep6_dispatch.go)
• Recipient handler hardcodes range count/size validation against compile-time constants -- The challenger reads StorageTruthCompoundRangesPerArtifact and StorageTruthCompoundRangeLenBytes from chain params, but the recipient validates against hardcoded LEP6CompoundRangesPerArtifact/LEP6CompoundRangeLenBytes; if governance updates these params, all compound challenges will silently fail (handler.go)

Previous reviews

• 8a80fc4: Review #1
• 820625c: Review #2

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