ci(4311): list fmt-affected files in job summary on drift

The cargo fmt gate already existed in ci-pr.yml, ci-main.yml, and
.gitea/workflows/native-ci.yml and was correctly wired into the merge
gate (ci-pr.yml:636). The one unmet AC of #4311 was 'lists the affected
files in the job summary' -- previously the step dumped only a raw
unified diff.

Replace the bare one-line Rustfmt Check with a step that captures the
diff, preserves the exit code (any non-zero cargo fmt exit propagates),
and on failure writes a deduplicated, repo-relative affected-files list
to $GITHUB_STEP_SUMMARY. Behaviour-preserving: still fails on drift,
still passes when clean (no summary written on the clean path).

Mirrored identically into ci-main.yml. The native .gitea workflow is
left untouched (Gitea Actions syntax, no step-summary support; its gate
goal of failing on drift is already met).

Verification (this session):
- drift path: exit 1, summary lists 4 files (deduped from 13 hunks),
  no stray commas (rendered output cat -A checked)
- clean path: exit 0, no summary written
- bash -n on extracted shipped body: SYNTAX OK
- python3 yaml.safe_load on both files: VALID
- rch exec exit-code propagation verified (true->0, false->1, fmt drift->1)

Out of scope (surgical): pre-existing fmt drift (#3013, owned by open
PR #3018) is NOT reformatted -- only the gate UX is changed.

Refs #4311

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Test User

.github/workflows/ci-main.yml

@@ -127,7 +127,28 @@ jobs:
           /home/alex/.local/bin/sccache --zero-stats
 
       - name: Rustfmt Check
-        run: /home/alex/.local/bin/rch exec -- cargo fmt --all -- --check
+        # Fail on drift (#4311) and list affected files in the job summary.
+        # Exit code is preserved: any non-zero cargo fmt exit propagates.
+        run: |
+          set +e
+          diff_output="$(/home/alex/.local/bin/rch exec -- cargo fmt --all -- --check 2>&1)"
+          fmt_exit=$?
+          if [ "$fmt_exit" -ne 0 ]; then
+            affected="$(printf '%s\n' "$diff_output" | grep '^Diff in ' | sed -E 's|^Diff in ||; s|:[0-9]+: *$||' | sort -u)"
+            rel="$(printf '%s\n' "$affected" | sed "s|^${GITHUB_WORKSPACE:-$PWD}/||")"
+            {
+              echo "## 🎨 cargo fmt drift detected"
+              echo ""
+              echo "Run \`cargo fmt --all\` locally and commit the result."
+              echo ""
+              echo "**Affected files ($(printf '%s\n' "$rel" | grep -c .)):**"
+              echo ""
+              printf -- '- \`%s\`\n' $rel
+              echo ""
+            } >> "$GITHUB_STEP_SUMMARY"
+            printf '%s\n' "$diff_output"
+            exit "$fmt_exit"
+          fi
 
       - name: Clippy Check
         # Soft-fail: terraphim_service registry crate has known compilation errors

.github/workflows/ci-pr.yml

@@ -199,7 +199,28 @@ jobs:
           /home/alex/.local/bin/sccache --zero-stats
 
       - name: Rustfmt Check
-        run: /home/alex/.local/bin/rch exec -- cargo fmt --all -- --check
+        # Fail on drift (#4311) and list affected files in the job summary.
+        # Exit code is preserved: any non-zero cargo fmt exit propagates.
+        run: |
+          set +e
+          diff_output="$(/home/alex/.local/bin/rch exec -- cargo fmt --all -- --check 2>&1)"
+          fmt_exit=$?
+          if [ "$fmt_exit" -ne 0 ]; then
+            affected="$(printf '%s\n' "$diff_output" | grep '^Diff in ' | sed -E 's|^Diff in ||; s|:[0-9]+: *$||' | sort -u)"
+            rel="$(printf '%s\n' "$affected" | sed "s|^${GITHUB_WORKSPACE:-$PWD}/||")"
+            {
+              echo "## 🎨 cargo fmt drift detected"
+              echo ""
+              echo "Run \`cargo fmt --all\` locally and commit the result."
+              echo ""
+              echo "**Affected files ($(printf '%s\n' "$rel" | grep -c .)):**"
+              echo ""
+              printf -- '- \`%s\`\n' $rel
+              echo ""
+            } >> "$GITHUB_STEP_SUMMARY"
+            printf '%s\n' "$diff_output"
+            exit "$fmt_exit"
+          fi
 
       - name: Clippy Check
         run: /home/alex/.local/bin/rch exec -- cargo clippy --workspace --all-targets --features zlob -- -D warnings