bazel: consume prebuilt wee8 in bzlmod (#47203)

## Commit Message
bazel: consume prebuilt wee8 in bzlmod

## Additional Description
Wires Envoy's **bzlmod** builds to consume the prebuilt V8 wee8 static
library (`libwee8.a`), mirroring what the WORKSPACE build already does
(shipped in #47108). This is the bzlmod counterpart of the WORKSPACE
wee8
prebuilt injection.

Changes:
- **Registry pin** ( `api/.bazelrc`) bumped to
  `4fb0f61a75eb72ffb0b7efaccc72dd9efb6a9dce`, which carries
proxy-wasm-cpp-host's `//bazel:v8_engine` `label_flag` — the bzlmod seam
  for redirecting the V8 engine (envoyproxy/bazel-registry#61).
- **`MODULE.bazel`** registers `wee8_prebuilt_extension` so the
`@wee8_prebuilt_*` repos exist under bzlmod (the extension equivalent of
  the WORKSPACE `setup_wee8_prebuilt()`).
- **Engine flag** pointed at `//bazel:wee8_engine` in `.bazelrc`, so
bzlmod
  builds select the prebuilt while reusing the existing alias that keeps
  gcc/sanitizer builds on the from-source engine.
- Regenerated the root/api/docs/mobile lockfiles.

In WORKSPACE mode the flag already defaults to
`@envoy//bazel:wee8_engine`
via `bazel/proxy_wasm_cpp_host.patch`; the shared `common` `.bazelrc`
line is
now safe in both modes because `//bazel:v8_engine` exists in the
registry
patch as well as the WORKSPACE patch.

## Risk Level
Low — bzlmod wiring only; WORKSPACE behavior unchanged. gcc/sanitizer
builds
continue to build V8 from source via the `wee8_engine` alias fallback.

## Testing
`bazel cquery --enable_bzlmod --noenable_workspace
'deps(@proxy-wasm-cpp-host//:v8_lib)'`
resolves to `@wee8_prebuilt_x86_64//:lib/libwee8.a` with **no**
from-source
`@v8//` remaining in the dep path. Lockfiles regenerated via
`bazel mod ... deps --lockfile_mode=update` (per `ci/do_ci.sh
lockfiles`).

## Docs Changes
N/A

## Release Notes
N/A

## Platform Specific Features
N/A

Signed-off-by: Dario Cillerai <dcillera@redhat.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>