ci: classify EchoEphapaxBridge in echo-kernel-note (kernel-guard fix)

Pre-existing CI invariant (`scripts/kernel-guard.sh` step B): every
`Echo*.agda` module must be classified somewhere in
`docs/echo-types/echo-kernel-note.adoc`. The initial #126 stub commit
landed the module but missed the classification, failing the kernel-
guard step before Agda's typecheck started.

Adds `EchoEphapaxBridge` to the Tier-2 list adjacent to
`EchoCNOBridge` (both are cross-repo bridges depending on Tier-2
`EchoLinear` / `EchoResidue`). No semantic change.

Local: `sh scripts/kernel-guard.sh` PASS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

docs/echo-types/echo-kernel-note.adoc

@@ -79,6 +79,7 @@ kernel** — the boundary is real and lives outside this core.
   `EchoEpistemicResidue`, `EchoExamples`, `EchoGraded`,
   `EchoLinear`, `EchoPullback`, `EchoRelModel`, `EchoScope`,
   `EchoStabilityTests`, `EchoThermodynamics`, `EchoCNOBridge`,
+  `EchoEphapaxBridge`,
   `EchoThermodynamicsFinite`, `EchoIntegration`, `EchoAccess`,
   `EchoCost`, `EchoCostInstance`, `EchoSearch`, `EchoSearchInstance`,
   `EchoExampleAbsInt`, `EchoExampleParser`, `EchoExampleProvenance`,