nebula-mesh: CA private key not zeroized on web mobile-bundle error paths

The web handler renderMobileBundle (internal/web/handlers.go:1325) passes the real *pki.CAResolver directly into mobilebundle.Build. Inside Build (internal/mobilebundle/builder.go:54), resolver.LoadByID decrypts the CA's ed25519 private key into a *pki.CAManager, but Build never calls CAManager.Wipe() on any return path (success or any of the error paths at lines 56, 62, 68, 80, 86, 92, 98, 102, 109, 118, 150).

As a result, when a mobile-bundle request goes through the web UI and Build returns — especially on error (missing network, invalid prefix, DB error, signing failure) — the plaintext CA private key remains on the Go heap, unwiped, until garbage collection. An attacker able to read process memory (core dump, swap, memory-scraping) can recover the CA signing key, which would allow minting arbitrary host certificates for the mesh.

The API handler (internal/api/mobile_bundle.go:74) already does this correctly: it loads the CAManager, defer caMgr.Wipe(), and wraps it in caManagerResolver. Only the web path is affected.

This is the same key-zeroization class previously addressed in GHSA-8h84-fhqq-q58v.

Add defer caMgr.Wipe() inside mobilebundle.Build immediately after the LoadByID call so every caller (web and API) is protected on all return paths. Ensure CAManager.Wipe() is idempotent, since the API handler also wipes the same manager.

None at the configuration level; requires a code fix.

• internal/web/handlers.go:1325
• internal/mobilebundle/builder.go:54
• internal/api/mobile_bundle.go:74 (correct reference implementation)
• Prior related advisory: GHSA-8h84-fhqq-q58v