ci: pin buf-action to 1.71.0 to match proto codegen

PR #2512 pinned the buf CLI in .github/workflows/buf.yml to 1.65.0, but
#2518 had already bumped codegen (BUF_VERSION in taskfiles/proto.yaml) to
1.71.0 and reformatted every proto with the 1.71.0 formatter. CI then
validated 1.71.0-formatted protos with buf 1.65.0, which re-expands the
nested message literals that 1.71.0 collapses, so buf format --diff failed
on master across ~30 protos.

Bump all three buf-action version pins to 1.71.0 so the CI format check
matches the committed protos and the codegen source of truth.

Verified locally against current master protos:
- buf 1.65.0 format --diff --exit-code: exit 100 (reproduces the failure)
- buf 1.71.0 format --diff --exit-code: clean

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: andrewhsu

.github/workflows/buf.yml

@@ -48,7 +48,7 @@ jobs:
         uses: bufbuild/buf-action@v1
         with:
           # buf CLI version - keep in sync with BUF_VERSION in taskfiles/proto.yaml
-          version: 1.65.0
+          version: 1.71.0
           lint: true
           format: true
           breaking: ${{ github.event_name == 'pull_request' && !contains(github.event.pull_request.labels.*.name, 'Buf Skip Breaking') }}
@@ -82,7 +82,7 @@ jobs:
         uses: bufbuild/buf-action@v1
         with:
           # buf CLI version - keep in sync with BUF_VERSION in taskfiles/proto.yaml
-          version: 1.65.0
+          version: 1.71.0
           # No validation - already done in validate job
           lint: false
           format: false
@@ -117,7 +117,7 @@ jobs:
         uses: bufbuild/buf-action@v1
         with:
           # buf CLI version - keep in sync with BUF_VERSION in taskfiles/proto.yaml
-          version: 1.65.0
+          version: 1.71.0
           # Only archive - no other operations
           push: true
           token: ${{ env.BUF_TOKEN }}