feat(sdd): add Gitea issue templates and SDD CI gate

Adds .gitea/ISSUE_TEMPLATE/{feature,bug}.md (the feature template mirrors the
EARS feature-spec) and .gitea/workflows/sdd-gate.yml — spec-lint, contract
validation (Spectral), traceability check (all non-blocking during adoption),
and a constitution-impact PR comment.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/ISSUE_TEMPLATE/feature.md

@@ -0,0 +1,82 @@
+---
+name: "Feature (SDD spec)"
+about: "Spec-driven feature request. Fill in EARS requirements before implementation starts."
+title: "As a <role> I want <capability> so <reason>"
+labels:
+  - spec-required
+  - needs-review
+assignees: []
+---
+
+<!--
+  This is a Spec-Driven feature spec. Mirror it to .specify/features/<name>/spec.md once the
+  feature has a working name. Every requirement uses an EARS pattern + a REQ-NNN id.
+  Reference: .specify/templates/feature-spec.md and the worked example .specify/features/_example/.
+  Delete the placeholder hints as you fill each section.
+-->
+
+## Context & Why
+
+<Who needs this and why now (2–4 sentences). Link the constitution principle(s) this depends on: .specify/constitution.md>
+
+## User Journey
+
+<Plain-prose steps the user takes to get value, from the user's perspective. Anything not here is out of scope.>
+
+## Requirements
+
+<!-- One per line, each REQ-NNN + one EARS pattern. A mutating feature needs at least one Event-driven and one Unwanted-behavior requirement. -->
+
+- **REQ-001** (Ubiquitous) — The `<component>` shall `<always-true behavior>`.
+- **REQ-002** (Event-driven) — When `<trigger>`, the `<component>` shall `<response>`.
+- **REQ-003** (State-driven) — While `<state>`, the `<component>` shall `<behavior>`.
+- **REQ-004** (Optional-feature) — Where `<caller has Permission.X / flag set>`, the `<component>` shall `<behavior>`.
+- **REQ-005** (Unwanted-behavior) — If `<undesired condition>`, then the `<component>` shall `<safe response / ErrorCode>`.
+
+## Acceptance Criteria
+
+<!-- One measurable criterion per REQ-NNN: numbers, limits, status codes — not adjectives. -->
+
+- **REQ-001** — <measurable>.
+- **REQ-002** — <measurable>.
+
+## Out of Scope
+
+- <The nearest tempting scope creep, named and excluded.>
+
+## API / Contract Stub
+
+<Inline stub or link to .specify/features/<name>/api-contract.yaml. Name new paths/methods/status codes and the @RequirePermission on each mutating endpoint.>
+
+## Data Model Changes
+
+<Schema delta + next free Flyway V<n> (verify on disk) + rollback note. "none" if not applicable.>
+
+## Security Considerations
+
+<STRIDE categories touched (+ ASTRIDE if an AI agent/tool is involved). Link a threat-model.md if the attack surface is non-trivial.>
+
+## Open Questions
+
+<!-- Each item BLOCKS implementation until resolved. -->
+
+- [ ] <question> — owner: <name>
+
+## Traceability
+
+| REQ-ID | Task ID(s) | Test ID(s) | Status |
+|---|---|---|---|
+| REQ-001 |  |  | Planned |
+
+<!-- Mirror these rows into .specify/rtm.md. -->
+
+## Persona Review Results
+
+| Persona | Status | Key Findings | Resolved |
+|---|---|---|---|
+| Requirements Engineer | PENDING |  |  |
+| Developer | PENDING |  |  |
+| Security | PENDING |  |  |
+| DevOps | PENDING |  |  |
+| UI/UX | PENDING |  |  |
+| Architect | PENDING |  |  |