vector: build weed-vector without a system protoc (#12317)

* vector: build without a system protoc

lance's build scripts run $PROTOC and fail without one. Point it at the
protoc that protoc-bin-vendored ships, at the version in Cargo.lock, so
building inside seaweed-vector/ needs only the Rust toolchain. An explicit
PROTOC still wins, and a registry without the crate falls back to PATH.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test(s3vectors): build weed-vector inside its workspace

Cargo reads seaweed-vector/.cargo/config.toml only when it runs there, so
build from that directory to pick up the vendored protoc.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* ci(vector): drop the PROTOC step the workspace config replaces

Builds run inside seaweed-vector/, where the cargo config already points
lance at the vendored protoc.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test(s3vectors): resolve CARGO_TARGET_DIR before changing directory

A relative CARGO_TARGET_DIR given to make would point cargo, which now runs
in seaweed-vector/, and the cp after it at different directories.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* vector: pick the vendored protoc on every Linux host it ships for

protoc-bin-vendored also carries ppc64le, s390x and x86_32 binaries.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/rust-vector-tests.yml

@@ -68,19 +68,6 @@ jobs:
           restore-keys: |
             rust-vector-${{ steps.toolchain.outputs.fingerprint }}-
 
-      # lance's build scripts compile their own protos and look for a protoc.
-      # Point them at the one protoc-bin-vendored ships, so no job depends on a
-      # system package and every build sees the same version.
-      - name: Use the vendored protoc
-        run: |
-          cd seaweed-vector
-          cargo fetch
-          version=$(awk '/^name = "protoc-bin-vendored-linux-x86_64"$/{found=1; next} found && /^version = /{gsub(/"/,"",$3); print $3; exit}' Cargo.lock)
-          test -n "$version" || { echo "protoc-bin-vendored-linux-x86_64 is not in Cargo.lock" >&2; exit 1; }
-          protoc=$(find ~/.cargo/registry/src -path "*protoc-bin-vendored-linux-x86_64-$version/bin/protoc" | head -1)
-          test -x "$protoc" || { echo "no vendored protoc $version in the registry" >&2; exit 1; }
-          echo "PROTOC=$protoc" >> "$GITHUB_ENV"
-
       - name: Build the vector crates
         run: cd seaweed-vector && cargo build --release
 
@@ -125,15 +112,6 @@ jobs:
           key: vectors-e2e-${{ runner.os }}-${{ runner.arch }}-${{ steps.toolchain.outputs.fingerprint }}-${{ hashFiles('seaweed-vector/Cargo.lock', 'seaweed-volume/Cargo.lock') }}
           restore-keys: |
             vectors-e2e-${{ runner.os }}-${{ runner.arch }}-${{ steps.toolchain.outputs.fingerprint }}-
-      - name: Use the vendored protoc
-        run: |
-          cd seaweed-vector
-          cargo fetch
-          version=$(awk '/^name = "protoc-bin-vendored-linux-x86_64"$/{found=1; next} found && /^version = /{gsub(/"/,"",$3); print $3; exit}' Cargo.lock)
-          test -n "$version" || { echo "protoc-bin-vendored-linux-x86_64 is not in Cargo.lock" >&2; exit 1; }
-          protoc=$(find ~/.cargo/registry/src -path "*protoc-bin-vendored-linux-x86_64-$version/bin/protoc" | head -1)
-          test -x "$protoc" || { echo "no vendored protoc $version in the registry" >&2; exit 1; }
-          echo "PROTOC=$protoc" >> "$GITHUB_ENV"
       - name: Test Go vector gateway
         run: |
           go test ./weed/s3api/s3vectors -count=1