feat(repo)!: restructure around the dsh-harness image and one example per implementation

- the root Dockerfile is the primary artifact; versions.env is the single source of truth
- merge gateway-api/dsh-demo into examples/dsh-agents-as-a-service (manifests/, exposure variants)
- move the single-tenant template into examples/minimal-single-tenant
- publish the gateway as a nested package under the repository image
- mirror the DSH ref for release identities (first release dsh-v0.2.1-rc.2-r2)
- CI: lint/python/manifests/gateway-image, reusable multi-arch build, tag-driven release, weekly e2e
- docs: README, docs/{main-image,examples,gitflow,versioning}, example READMEs, AGENTS.md, governance
- SSO is opt-in again; gateway pull policy and cookie defaults match the documented demo

BREAKING CHANGE: example manifest paths, the gateway image name, and the removal
of deploy/ and gateway-api/ affect existing deployments; see the migration table
in README.md.

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,35 @@
+name: Feature request
+description: Propose a new example, image capability or workflow improvement.
+labels: ["enhancement"]
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem or use case
+      description: What are you trying to do, and what blocks you today?
+    validations:
+      required: true
+  - type: textarea
+    id: proposal
+    attributes:
+      label: Proposed solution
+      description: Describe the shape you have in mind. For a new example, say which implementation it demonstrates.
+    validations:
+      required: true
+  - type: dropdown
+    id: area
+    attributes:
+      label: Area
+      options:
+        - Main DSH Web image
+        - Existing example
+        - New example
+        - CI / release automation
+        - Documentation
+        - Other
+    validations:
+      required: true
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives considered