[SIMPL-30451] Add distributed-execution service with guide and reference implementations

Canonical location for documentation, example workflows and reference service implementations covering distributed execution patterns. Covers AC1-AC4: execution-target selection, decision support, readiness checks and code-level linkage. Tightly coupled jobs and the loosely coupled subprocess transport are verified by the test suite; the Kubernetes pipes transport is implemented but not yet cluster-run and is marked as such in the guide.

Changelog: added

yaml/tightly-coupled/values-run-launcher.yaml

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+# Tightly coupled execution target - instance-level run launcher.
+#
+# Merge into the Dagster chart values. This is the half of the execution-target
+# binding that lives OUTSIDE workflow code: it decides where the run worker for
+# an entire run is placed, and what that pod can reach.
+#
+# Companion to src/distributed_execution/tightly_coupled/jobs.py, which decides
+# how the steps INSIDE that run worker execute.
+
+dagster:
+  runLauncher:
+    type: K8sRunLauncher
+    config:
+      k8sRunLauncher:
+        # Namespace the run pods land in. Must be a namespace whose NetworkPolicy
+        # permits egress to Postgres, object storage and Vault - see AC1
+        # prerequisites in the user guide.
+        jobNamespace: dagster
+
+        # Surfaces step failures as pod failures so kubectl and Dagster agree.
+        failPodOnRunFailure: true
+
+        runK8sConfig:
+          podTemplateSpecMetadata:
+            annotations:
+              vault.security.banzaicloud.io/vault-inject: "true"
+              vault.security.banzaicloud.io/vault-addr: https://secrets.common01.dev.simpl-europe.eu
+              vault.security.banzaicloud.io/vault-role: dev-role
+              vault.security.banzaicloud.io/vault-skip-verify: "true"
+              vault.security.banzaicloud.io/vault-path: kubernetes
+
+          containerConfig:
+            resources:
+              requests:
+                cpu: 100m
+                memory: 128Mi
+              limits:
+                cpu: 500m
+                memory: 512Mi
+
+            # Everything below is what "tightly coupled" costs you: each run pod
+            # needs credentials for, and network reachability to, the full
+            # orchestration runtime. A loosely coupled target needs none of it.
+            env:
+              - name: DAGSTER_TELEMETRY_ENABLED
+                value: "false"
+              - name: TOKEN
+                value: "vault:dev/data/dagster/dagster-workflow-vault-secret#VAULT_ACCESS_TOKEN"
+              - name: S3_ENDPOINT_URL
+                value: "https://s3.dev.simpl-europe.eu"
+              - name: S3_ACCESS_KEY
+                value: "vault:dev/data/dev-orchestration-platform#S3_ACCESS_KEY"
+              - name: S3_SECRET_KEY
+                value: "vault:dev/data/dev-orchestration-platform#S3_SECRET_KEY"