feat(chain): add freeze_height to the unified schema

[bdchatham]

What this does

Adds chain.freeze_height to the unified schema, so a caller can set seid's
freeze-height declaratively.

seid reads freeze-height from app.toml to stop executing at a height while
still serving query RPC. The key was missing from this schema, so
ApplyOverrides rejected it as an unknown key (io.go) and no caller could set
it. That closes the only declarative route: sei-k8s-controller builds a fixed
seid start --home <dataDir> argv with no flag escape hatch, so the config file
is the only way in.

Why it is shaped like halt_height

halt_height is the direct precedent — it sits beside freeze-height in the
same sei-cosmos BaseConfig. This change mirrors it exactly:

Site	Change
config.go	FreezeHeight uint64 on ChainConfig, unified key chain.freeze_height
legacy.go	legacy app.toml key freeze-height on legacyAppConfig
legacy.go	both mappings — toLegacyApp() and fromLegacy()
enrichments.go	description and blocks unit
validate.go	the two rules seid enforces
freeze_test.go	round-trip, override, and a validation table

Two judgment calls

No baseDefaults() entry. HaltHeight and HaltTime have none either —
zero already means disabled, and the zero value delivers that. The repo guide
says to add a default for a new field; the established pattern for this exact
kind of field says otherwise, so I followed the pattern. Say the word if you
want it stated explicitly instead.

Tests in a new file. config_test.go is at 884 lines, past the ~500-line
threshold in the repo guide, so the new coverage went to freeze_test.go.

Validation

validate.go now mirrors seid's own ValidateFreeze, so an invalid combination
is reported here instead of failing at node start:

• freeze_height must fit in an int64. seid converts it and rejects an
  over-range value.
• freeze_height cannot be combined with halt_height or halt_time. Freeze
  keeps serving queries; halt exits the process.

I did not port seid's third rule — freeze-height cannot be used with
grpc-only. That one reads a CLI flag, not config, so it has no representation
here.

Testing

Check	Result
make test	ok
go vet ./...	clean
staticcheck ./...	clean
gofmt -l .	clean
golangci-lint run	47 issues on this branch, 47 on origin/main, identical breakdown — none introduced

I checked out origin/main to take that lint baseline rather than assume it.
Note the repo does not pass golangci-lint 2.12.2 even on main, so CI is
pinning an older version.

New coverage:

• TestFreezeHeight_RoundTrip — asserts the rendered app.toml carries the
  freeze-height spelling seid actually reads, then reads it back.
• TestFreezeHeight_Override — the chain.freeze_height override path the
  controller and seictl use.
• TestFreezeHeight_Validate — 6 cases: unset, freeze alone, halt alone, freeze
  with halt height, freeze with halt time, and int64 overflow.

Follow-ups, not in this PR

• A release commit to bump version.json, per the convention here.
• sei-sidecar bumps this library. That is the load-bearing consumer — it runs
  the override resolution and validation.
• sei-k8s-controller bumps it for hygiene only. It never validates or writes
  config; it uses this library for types and constants, merges spec.overrides,
  and forwards the map verbatim. No CRD change is needed, because
  spec.overrides is already a free-form map[string]string.

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Schema and validation-only extension with tests; no runtime node behavior changes in this repo.

Overview
Adds chain.freeze_height to the unified Sei config so operators can set seid’s freeze-height (stop block execution at a height while keeping query RPC) via overrides and generated app.toml, matching how halt_height works.

The field is wired through ChainConfig, legacy app.toml read/write (freeze-height), schema enrichments, and Validate rules aligned with seid: value must fit in int64, and freeze_height cannot be set together with halt_height or halt_time. New tests cover app.toml round-trip, ApplyOverrides, and those validation cases.

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