feat: type-generic registry for cross-service read-your-writes subscriptions

The shared core of Shiny's cross-service read-your-writes GraphQL subscriptions
(ADR-0012), extracted and hardened from the near-identical hand-rolled handlers
in authz-service (availableCompanies) and accounting-service (entryBasesChanged)
before a third copy is written.

Registry[T] owns the keyed subscriber map, non-blocking buffered fan-out (sends
under the read lock so a close can't race a send), a key-sharded worker pool that
runs the read-view gate OFF the AMQP delivery goroutine (preserving per-key FIFO
order while distinct keys run in parallel), the bounded retry/timeout budget, and
Observer metric hooks. Services supply only the event->key+payload mapping, the
read-view Producer closure, and the per-replica transient-consumer wiring.

Reviewed pre-publish (Go + Event Sourcing + Architecture). 99% coverage, race-clean.

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

.gitea/workflows/ci.yaml

@@ -0,0 +1,107 @@
+name: subscriptions
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    if: gitea.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
+        with:
+          go-version: 'stable'
+      - name: Format check
+        run: |
+          go install mvdan.cc/gofumpt@latest
+          test -z "$(gofumpt -l .)"
+      - name: Run tests
+        run: go test -race -coverprofile=coverage.txt ./...
+
+      - name: Filter test files from coverage
+        run: |
+          grep -v -E '_test\.go:' coverage.txt > coverage.filtered.txt || true
+          mv coverage.filtered.txt coverage.txt
+
+      - name: Check coverage
+        id: coverage
+        run: |
+          go install github.com/vladopajic/go-test-coverage/v2@latest
+          go-test-coverage --config ./.testcoverage.yml --github-action-output
+      - name: Restore baseline coverage
+        uses: actions/cache/restore@v5
+        with:
+          path: coverage-baseline.txt
+          key: coverage-baseline-${{ gitea.run_id }}
+          restore-keys: |
+            coverage-baseline-
+      - name: Compare coverage
+        run: |
+          CURRENT="${{ steps.coverage.outputs.total-coverage }}"
+          if [ -f coverage-baseline.txt ]; then
+            BASE=$(cat coverage-baseline.txt)
+            echo "Base coverage: ${BASE}%"
+            echo "Current coverage: ${CURRENT}%"
+            if [ "$(echo "$CURRENT < $BASE" | bc -l)" -eq 1 ]; then
+              echo "::error::Coverage decreased from ${BASE}% to ${CURRENT}%"
+              exit 1
+            fi
+            echo "Coverage maintained or improved: ${BASE}% -> ${CURRENT}%"
+          else
+            echo "No baseline coverage found yet, skipping comparison"
+            echo "Current coverage: ${CURRENT}%"
+          fi
+      - name: Post coverage comment
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          GITEA_URL: ${{ gitea.server_url }}
+        run: |
+          COVERAGE="${{ steps.coverage.outputs.total-coverage }}"
+          curl -X POST "${GITEA_URL}/api/v1/repos/${{ gitea.repository }}/issues/${{ gitea.event.pull_request.number }}/comments" \
+            -H "Authorization: token ${GITEA_TOKEN}" \
+            -H "Content-Type: application/json" \
+            -d "{\"body\": \"## Coverage Report\n\nTotal coverage: **${COVERAGE}%**\"}"
+
+  coverage-baseline:
+    # Records main's coverage into the Actions cache for the next PR's
+    # regression gate to read. Post-merge only, not a required check, blocks
+    # nothing (cf. ADR-0010).
+    if: gitea.event_name == 'push'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
+        with:
+          go-version: 'stable'
+      - name: Compute coverage
+        id: coverage
+        run: |
+          go install github.com/vladopajic/go-test-coverage/v2@latest
+          go test -coverprofile=coverage.txt ./...
+          grep -v -E '_test\.go:' coverage.txt > coverage.filtered.txt || true
+          mv coverage.filtered.txt coverage.txt
+          go-test-coverage --config ./.testcoverage.yml --github-action-output
+      - name: Write baseline file
+        run: echo "${{ steps.coverage.outputs.total-coverage }}" > coverage-baseline.txt
+      - name: Save baseline to cache
+        uses: actions/cache/save@v5
+        with:
+          path: coverage-baseline.txt
+          key: coverage-baseline-${{ gitea.run_id }}
+
+  vulnerabilities:
+    if: gitea.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
+        with:
+          go-version: 'stable'
+      - name: Check vulnerabilities
+        run: |
+          go install golang.org/x/vuln/cmd/govulncheck@latest
+          govulncheck ./...