clusterversion: enable 25.4 upgrade tests (M.3)

This change implements M.3 "Enable upgrade tests" from the quarterly
release runbook, enabling roachtest upgrade tests with version 25.4 after
the first RC (v25.4.0-rc.1) was published.

This was done as a single combined PR (Approach B) rather than splitting
into separate fixtures and code PRs.

Changes include:

**1. Update releases and binaries:**
- Updated releases file with v25.4.0-rc.1 via release tool
- Updated REPOSITORIES.bzl with RC binaries for all platforms

**2. Generate roachtest fixtures (on gceworker):**
- Added 4 fixture files (checkpoint-v25.4.tgz) for nodes 1-4
- Fixtures were generated on gceworker (amd64 required) by running:
    ./bin/roachtest run generate-fixtures --local --debug \
      --cockroach ./cockroach --suite fixtures
- Total fixture size: ~15.5 MB (4.4M + 4.2M + 3.7M + 2.8M)

**3. Update PreviousRelease constant:**
- Changed from V25_3 to V25_4 in cockroach_versions.go
- This enables upgrade testing from the 25.4 release

**4. Add cockroach-go-testserver-25.4 configuration:**
- Added testserver config in logictestbase.go
- Added to cockroach-go-testserver-configs set
- Updated BUILD.bazel visibility for the new config

**5. Generate test files:**
- Generated cockroach-go-testserver-25.4 test files via ./dev gen bazel
- Updated pkg/BUILD.bazel

**6. Add comprehensive M.3 runbook:**
- Added detailed step-by-step M.3 documentation to CLAUDE.md
- Covers both two-PR (Approach A) and single-PR (Approach B) methods
- Includes gceworker setup, fixture generation, validation steps
- Documents common errors and solutions

Files modified: 12 files (~1108 insertions, ~10 deletions)
- pkg/BUILD.bazel (binary)
- pkg/clusterversion/CLAUDE.md (+927 lines - M.3 runbook)
- pkg/clusterversion/cockroach_versions.go (PreviousRelease)
- pkg/cmd/roachtest/fixtures/*/checkpoint-v25.4.tgz (4 new files)
- pkg/sql/logictest/REPOSITORIES.bzl (RC binaries)
- pkg/sql/logictest/logictestbase/logictestbase.go (testserver config)
- pkg/sql/logictest/tests/cockroach-go-testserver-25.4/* (generated)
- pkg/testutils/release/cockroach_releases.yaml (v25.4.0-rc.1)

Part of the quarterly release runbook M.3 checklist.

Release note: None
Epic: None

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: celiala

pkg/BUILD.bazel

@@ -520,6 +520,7 @@ ALL_TESTS = [
     "//pkg/sql/logictest/tests/5node:5node_test",
     "//pkg/sql/logictest/tests/cockroach-go-testserver-25.2:cockroach-go-testserver-25_2_test",
     "//pkg/sql/logictest/tests/cockroach-go-testserver-25.3:cockroach-go-testserver-25_3_test",
+    "//pkg/sql/logictest/tests/cockroach-go-testserver-25.4:cockroach-go-testserver-25_4_test",
     "//pkg/sql/logictest/tests/fakedist-disk:fakedist-disk_test",
     "//pkg/sql/logictest/tests/fakedist-vec-off:fakedist-vec-off_test",
     "//pkg/sql/logictest/tests/fakedist:fakedist_test",
@@ -2095,6 +2096,7 @@ GO_TARGETS = [
     "//pkg/sql/logictest/tests/5node:5node_test",
     "//pkg/sql/logictest/tests/cockroach-go-testserver-25.2:cockroach-go-testserver-25_2_test",
     "//pkg/sql/logictest/tests/cockroach-go-testserver-25.3:cockroach-go-testserver-25_3_test",
+    "//pkg/sql/logictest/tests/cockroach-go-testserver-25.4:cockroach-go-testserver-25_4_test",
     "//pkg/sql/logictest/tests/fakedist-disk:fakedist-disk_test",
     "//pkg/sql/logictest/tests/fakedist-vec-off:fakedist-vec-off_test",
     "//pkg/sql/logictest/tests/fakedist:fakedist_test",