governance: external contribution model (issues/discussions/RFCs/PRs) (#143)

Formalize the public contribution surface. Maintainers keep a separate internal
process and are exempt from the intake gates; everyone stays bound by review,
CODEOWNERS, and branch protection.

Model:
- Issues = problem reports only (bug form + config.yml redirects ideas to
  Discussions and disables blank issues).
- Discussions = ideas + RFC incubation.
- RFCs = anyone (incl. external) authors docs/rfcs/NNNN-*.md; a maintainer
  merging it is acceptance. Distinct from the maintainer-internal
  docs/dev/rfc-00N-* track.
- PRs = link an `accepted` issue or accepted RFC, or use the trivial fast-lane
  (typos/docs/deps). Enforced softly to start (template + review).

Adds GOVERNANCE.md, rewrites CONTRIBUTING.md, adds docs/rfcs/ (README +
template), .github issue/PR/discussion templates. Wires docs/rfcs/ into the
doc-link checker (excluded like releases; linked from docs/dev/index.md).

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

.github/DISCUSSION_TEMPLATE/rfc.yml

@@ -0,0 +1,34 @@
+labels: ["rfc"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Use this to **incubate an RFC** — socialize a design and reach rough
+        consensus before writing the formal document. When it's ready, graduate
+        it into a pull request that adds `docs/rfcs/NNNN-title.md`
+        (see [docs/rfcs/README.md](../blob/main/docs/rfcs/README.md)); a
+        maintainer merging that PR is acceptance.
+
+        For a plain feature request or open-ended idea, use the **Ideas**
+        category instead. For bugs, open an [Issue](../../issues/new/choose).
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem / motivation
+      description: What needs solving, and why is it worth the long-run cost?
+    validations:
+      required: true
+  - type: textarea
+    id: sketch
+    attributes:
+      label: Proposed direction (sketch)
+      description: A rough shape of the design. Detail comes later in the RFC document.
+    validations:
+      required: true
+  - type: textarea
+    id: invariants
+    attributes:
+      label: Invariants touched
+      description: Which items in docs/dev/invariants.md does this affect or risk? Any deny-list brush?
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -0,0 +1,55 @@
+name: Bug report
+description: Report a reproducible problem or wrong behavior in OmniGraph.
+title: "bug: <short summary>"
+labels: ["bug", "needs-triage"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Issues are for **reporting problems** — concrete, reproducible bugs.
+        For ideas, feature requests, or questions, please use
+        [Discussions](../../discussions) instead.
+        For a security vulnerability, follow [SECURITY.md](../../blob/main/SECURITY.md) — do **not** file it here.
+
+        A maintainer will triage this; once labelled **`accepted`** it's open for a pull request
+        (see [GOVERNANCE.md](../../blob/main/GOVERNANCE.md)).
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: What happened
+      description: What went wrong, and what you expected instead.
+    validations:
+      required: true
+  - type: textarea
+    id: repro
+    attributes:
+      label: Steps to reproduce
+      description: Minimal steps, commands, schema/query, or a failing snippet.
+      placeholder: |
+        1. omnigraph init ...
+        2. omnigraph ...
+        3. observed: ...  / expected: ...
+    validations:
+      required: true
+  - type: input
+    id: version
+    attributes:
+      label: Version
+      description: Output of `omnigraph --version` (or the engine/crate version) and how you installed it.
+    validations:
+      required: true
+  - type: input
+    id: environment
+    attributes:
+      label: Environment
+      description: OS, architecture, and storage backend (local FS / S3 / RustFS / MinIO).
+    validations:
+      required: false
+  - type: textarea
+    id: logs
+    attributes:
+      label: Logs / output
+      description: Relevant error text or logs. Will be rendered as code.
+      render: shell
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,13 @@
+# Issues are for problem reports only. Disable blank issues so everything is
+# routed: bugs through the form, everything else to Discussions / SECURITY.md.
+blank_issues_enabled: false
+contact_links:
+  - name: 💡 Idea, feature request, or RFC
+    url: https://github.com/ModernRelay/omnigraph/discussions
+    about: Propose features and designs in Discussions. RFCs graduate from there into a docs/rfcs/ pull request.
+  - name: ❓ Question or help
+    url: https://github.com/ModernRelay/omnigraph/discussions
+    about: Ask in Discussions — questions are not tracked as Issues.
+  - name: 🔒 Security vulnerability
+    url: https://github.com/ModernRelay/omnigraph/blob/main/SECURITY.md
+    about: Report security issues privately per SECURITY.md — never as a public Issue.

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,29 @@
+<!--
+  Thanks for contributing! See CONTRIBUTING.md and GOVERNANCE.md.
+  A substantive PR needs a backing accepted issue or accepted RFC.
+  Maintainers: your internal process applies; the link requirement below
+  is for external contributions.
+-->
+
+## What & why
+
+<!-- One or two sentences: what this changes and why. -->
+
+## Backing issue / RFC
+
+<!-- Pick one. A substantive change needs (1) or (2). -->
+
+- [ ] Fixes an **accepted** issue: Closes #
+- [ ] Implements / is an **accepted** RFC: <link to docs/rfcs/NNNN-*.md>
+- [ ] **Trivial fast-lane** (typo / docs / dependency bump / comment / one-line CI) — no issue/RFC required
+
+## Checklist
+
+- [ ] Change is focused (one logical change)
+- [ ] Tests added/updated for behavior changes (or N/A)
+- [ ] Public docs updated if user-facing surface changed (or N/A)
+- [ ] Reviewed against [docs/dev/invariants.md](../blob/main/docs/dev/invariants.md) — no Hard Invariant weakened, no deny-list item hit (or justified)
+
+## Notes for reviewers
+
+<!-- Anything that helps review: tradeoffs, follow-ups, areas of risk. -->