GHSA-2p2f-px33-4vv5

## Impact

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.

## Patches

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.

## Workarounds

None at the configuration level; requires a code fix.

## Resources

- `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