ci(release): enforce BTrace 3.0 RC gates

[jbachorik]

Closes #881

Stack/dependencies:

• Base PR: [3.0] Add acquisition-path and first-trace smoke tests #903 ([3.0] Add acquisition-path and first-trace smoke tests #880)
• Also requires fix(fat-agent): execute bundled probes end to end #899 ([3.0] Make Gradle fat-agent bundled probes execute end to end #878 bundled probes) and fix(maven): remove unpublished fat-agent module #900 ([3.0] Repair or explicitly withdraw Maven fat-agent support #879 Maven fat-agent removal)
• Validated locally on a disposable aggregate containing all [3.0] Decide prepared-agent security and client compatibility policy #872–[3.0] Add acquisition-path and first-trace smoke tests #880 changes.

What changed:

• Records exact focused-module, Gradle-plugin, Spotless, clean masked-JAR, distribution, and per-JDK integration commands with full logs and filtered job summaries.
• Expands the runtime matrix to JDK 8, 11, 17, 21, 25, and OpenJDK 27 EA, with an executable warning-policy probe.
• Makes missing Maven and GitHub release artifacts release-blocking and includes all release jobs in the final summary.
• Adds the 3.0 RC checklist covering security behavior, protocol negotiation, five incident-kit launch paths, acquisition surfaces, and explicit go/no-go exceptions.
• Removes the dead registry configuration fields and placeholder registry tests; registry sources are not part of the supported 3.0 Gradle DSL.
• Keeps the unpublished Maven fat-agent module removed by fix(maven): remove unpublished fat-agent module #900 and adds a release gate preventing its return.

Validation:

• Full standalone Gradle-plugin suite: PASS (21 tests)
• Focused core/agent/client suites: PASS
• Repository Spotless: PASS
• Clean :btrace-dist:btraceJar: PASS
• Full :btrace-dist:build: PASS
• Full integration suite after distribution build: PASS (8m10s)
• Live release smoke (telemetry, prepared auth/listener, doctor, noServer, permissions, V1/V2/auto): PASS
• Release artifact verifier: PASS
• Warning policy on JDK 8/11/17/21/25/27 EA: PASS (one warning on 8/11, zero on 17+)
• Gate recorder adversarial success/failure exit propagation: PASS
• Workflow YAML, shell syntax, and git diff --check: PASS

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This change is