Add frozen RPC router and Docker integration cluster

[codchen]

Describe your changes and provide context

• Add frozen-rpc-router, an EVM JSON-RPC proxy that routes block-scoped requests to the matching frozen node and all other traffic to the live node.
• Add a Docker Compose topology with non-validating archival nodes frozen before heights 10 and 20, two live validators, and the router exposed on port 8553.
• Add integration coverage that proves heights 9, 15, and 20 reach the height-10 frozen node, height-20 frozen node, and live node respectively, and verifies that cross-node block ranges are rejected.
• Build and package the router alongside seid, and add the topology to the integration-test CI matrix.

Testing performed to validate your change

• make frozen-rpc-router-integration-test
• go test -race ./cmd/frozen-rpc-router
• go test -tags frozen_rpc_integration -run '^$' ./integration_test/frozen_rpc_router/...
• golangci-lint run --build-tags frozen_rpc_integration ./cmd/frozen-rpc-router/... ./integration_test/frozen_rpc_router/...
• make fmtcheck
• git diff --check

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Aug 24, 2026, 1:28 PM

[codecov]

Codecov Report

❌ Patch coverage is 59.95935% with 197 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.89%. Comparing base (73f917b) to head (689f7d6).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/frozen-rpc-router/router.go	63.76%	96 Missing and 54 partials ⚠️
cmd/frozen-rpc-router/main.go	0.00%	39 Missing ⚠️
cmd/frozen-rpc-router/config.go	79.48%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3989      +/-   ##
==========================================
- Coverage   58.98%   57.89%   -1.10%     
==========================================
  Files        2310     2214      -96     
  Lines      197500   186422   -11078     
==========================================
- Hits       116487   107921    -8566     
+ Misses      70256    68625    -1631     
+ Partials    10757     9876     -881     

Flag	Coverage Δ
sei-chain-pr	59.95% <59.95%> (?)
sei-db	69.80% <ø> (ø)
sei-db-state-db	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cmd/frozen-rpc-router/config.go	79.48% <79.48%> (ø)
cmd/frozen-rpc-router/main.go	0.00% <0.00%> (ø)
cmd/frozen-rpc-router/router.go	63.76% <63.76%> (ø)

... and 99 files with indirect coverage changes

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