docs(ci): establish the GravityGraph v2 Stage 0 baseline

.github/ISSUE_TEMPLATE/v1-v2-work.yml

@@ -0,0 +1,58 @@
+name: V1/v2 tracked work
+description: Route v1 maintenance, v2, synchronization, release, or cutover work
+title: ""
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Read the [v1/v2 routing runbook](https://github.com/gravity-ui/graph/blob/main/docs/contributing/v1-v2-routing.md) before choosing a work type.
+  - type: dropdown
+    id: work-type
+    attributes:
+      label: Work type
+      description: Select the line or operation that owns this work.
+      options:
+        - v1-maintenance
+        - v2
+        - sync
+        - release-v1
+        - release-v2
+        - cutover
+    validations:
+      required: true
+  - type: dropdown
+    id: phase
+    attributes:
+      label: Project phase
+      options:
+        - Before v2 cutover
+        - After v2 cutover
+    validations:
+      required: true
+  - type: input
+    id: target
+    attributes:
+      label: Target branch
+      description: State the branch selected using the runbook.
+      placeholder: main, v2, or release/v1
+    validations:
+      required: true
+  - type: textarea
+    id: scope
+    attributes:
+      label: Scope and routing rationale
+      description: Explain why this work belongs to the selected line.
+    validations:
+      required: true
+  - type: textarea
+    id: evidence
+    attributes:
+      label: Required evidence
+      description: For sync/release/cutover work, include owners, SHAs, PRs, workflow runs, preview destinations, and verification as applicable.
+  - type: checkboxes
+    id: confirmation
+    attributes:
+      label: Confirmation
+      options:
+        - label: I followed the v1/v2 routing runbook and did not infer a branch or release channel from an unavailable future configuration.
+          required: true

.github/pull_request_template.md

@@ -0,0 +1,40 @@
+## Summary
+
+<!-- Describe the change and why it is needed. -->
+
+## V1/v2 routing
+
+- Work type: <!-- v1-maintenance | v2 | sync | release-v1 | release-v2 | cutover -->
+- Project phase: <!-- before v2 cutover | after v2 cutover -->
+- Target branch:
+- Routing rationale:
+
+Follow the
+[v1/v2 contribution and synchronization runbook](https://github.com/gravity-ui/graph/blob/main/docs/contributing/v1-v2-routing.md).
+
+## Verification
+
+- Checks run:
+- Workflow or preview evidence, when applicable:
+
+## Synchronization record
+
+<!-- Complete for sync work; otherwise write "Not applicable". -->
+
+- Owner:
+- Source v1 branch:
+- Full source SHA:
+- Applicability: <!-- port | no-port -->
+- Rationale:
+- Sync PR or no-port record:
+- Resulting merge SHA:
+- V2 conflict resolution or neutralization:
+- Verification:
+
+## Checklist
+
+- [ ] The selected target branch matches the current project phase and work type.
+- [ ] V1 changes are limited to necessary bug fixes, security fixes, or v1 documentation.
+- [ ] A synchronization PR uses a merge commit; squash, rebase, and cherry-pick are not used as the canonical branch sync.
+- [ ] Release and preview evidence uses the configured route and does not assume an undocumented destination.
+- [ ] This change does not treat v2 cutover as formal v1 deprecation or workflow retirement.

.github/release-routing/routes.json

@@ -0,0 +1,52 @@
+{
+  "activePhase": "pre-cutover",
+  "branchCreationPolicy": "skip-release-job",
+  "releaseRoutes": {
+    "pre-cutover-v1": {
+      "phase": "pre-cutover",
+      "branch": "main",
+      "major": 1,
+      "prerelease": false,
+      "distTag": "latest",
+      "workflow": "release-v1.yml",
+      "active": true
+    },
+    "pre-cutover-v2": {
+      "phase": "pre-cutover",
+      "branch": "v2",
+      "major": 2,
+      "prerelease": true,
+      "distTag": "next",
+      "workflow": "release-v2.yml",
+      "active": true
+    },
+    "post-cutover-v1": {
+      "phase": "post-cutover",
+      "branch": "release/v1",
+      "major": 1,
+      "prerelease": false,
+      "distTag": "v1",
+      "workflow": "release-v1.yml",
+      "active": false
+    },
+    "post-cutover-v2": {
+      "phase": "post-cutover",
+      "branch": "main",
+      "major": 2,
+      "prerelease": false,
+      "distTag": "latest",
+      "workflow": "release-v2.yml",
+      "active": false
+    }
+  },
+  "previewRoutes": {
+    "main": {
+      "workflow": "main-preview.yml",
+      "destination": "/graph/main/"
+    },
+    "v2": {
+      "workflow": "v2-preview.yml",
+      "destination": "/graph/v2/"
+    }
+  }
+}