feat(sdd): add .specify scaffold — constitution, AGENTS, personas, templates, example, RTM

Introduces the SDD root: a v1.0.0 constitution and machine-readable AGENTS.md
grounded in the project's real conventions; six EARS-aware persona spec-review
checklists that cross-reference .claude/personas/; feature-spec/ADR/threat-model/
api-contract templates; a fully worked _example feature; a living RTM; and an
adrs/ pointer that reuses the existing docs/adr/ archive.

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

.specify/templates/feature-spec.md

@@ -0,0 +1,89 @@
+<!--
+  Feature Spec template — copy this into a Gitea issue body (or .specify/features/<name>/spec.md).
+  Replace every <placeholder>. Delete this comment block before submitting.
+  EARS = Easy Approach to Requirements Syntax. Every requirement uses one of the five patterns
+  shown in ## Requirements and carries a unique REQ-NNN id (three-digit, scoped to THIS feature).
+  Companion artifacts live beside this file: design.md, api-contract.yaml, threat-model.md,
+  adr-NNN-*.md, tasks.md, checklist-results.md.
+-->
+
+# <Feature title — match the Gitea issue: "As a <role> I want <capability> so <reason>">
+
+## Context & Why
+
+<Business motivation in 2–4 sentences: who needs this and why now.>
+
+Constitution principles this feature depends on:
+- [§<n> <principle name>](../../constitution.md#<anchor>) — <why it applies>
+
+Related: <links to prior issues / ADRs / specs>.
+
+## User Journey
+
+<Plain-prose steps the user takes to get value, from the user's perspective — per COLLABORATING.md. Anything not in this journey is out of scope.>
+
+## Requirements
+
+> One requirement per line, each with a `REQ-NNN` id and one EARS pattern. Include the
+> patterns the feature actually needs — do not force all five, but a mutating feature almost
+> always needs at least one Event-driven and one Unwanted-behavior requirement.
+
+- **REQ-001** (Ubiquitous) — The `<system component>` shall `<always-true behavior>`.
+- **REQ-002** (Event-driven) — When `<trigger / endpoint receives X>`, the `<system component>` shall `<response>`.
+- **REQ-003** (State-driven) — While `<system is in state X>`, the `<system component>` shall `<behavior>`.
+- **REQ-004** (Optional-feature) — Where `<the caller has Permission.X / a feature flag is set>`, the `<system component>` shall `<behavior>`.
+- **REQ-005** (Unwanted-behavior) — If `<undesired condition, e.g. caller is unauthenticated / input invalid>`, then the `<system component>` shall `<safe response, e.g. return 401 / ErrorCode.X>`.
+
+## Acceptance Criteria
+
+> One measurable criterion per REQ-NNN. Numbers, limits, status codes — never adjectives.
+
+- **REQ-001** — <measurable, e.g. "the response always includes a non-null `id` (UUID)">.
+- **REQ-002** — <measurable, e.g. "POST returns 201 and the persisted row within the same request">.
+- **REQ-003** — <measurable>.
+- **REQ-004** — <measurable, e.g. "a caller without Permission.X receives 403 with ErrorCode.FORBIDDEN">.
+- **REQ-005** — <measurable, e.g. "an unauthenticated request receives 401 and nothing is persisted">.
+
+## Out of Scope
+
+- <Explicit boundary statement — the nearest tempting scope creep, named and excluded.>
+- <…>
+
+## API / Contract Stub
+
+<Inline stub OR link to `./api-contract.yaml`. Name the new/changed paths, methods, request/response shapes, status codes, and `@RequirePermission`.>
+
+## Data Model Changes
+
+<Entity/schema delta: new tables/columns, constraints, the next free Flyway `V<n>`, and the rollback note. Write "none" if not applicable.>
+
+## Security Considerations
+
+<STRIDE categories touched (Spoofing/Tampering/Repudiation/Information disclosure/DoS/Elevation). For AI-agent/tool features, also ASTRIDE. Link to `./threat-model.md` if the feature has a non-trivial attack surface.>
+
+## Open Questions
+
+> Each item is a BLOCKER until resolved. Empty this list before implementation starts.
+
+- [ ] <question> — owner: <name>
+- [ ] <question> — owner: <name>
+
+## Traceability
+
+| REQ-ID | Task ID(s) | Test ID(s) | Status |
+|---|---|---|---|
+| REQ-001 | <T-1> | <test name> | Planned |
+| REQ-002 | <T-2> | <test name> | Planned |
+
+<Mirror these rows into [.specify/rtm.md](../../rtm.md). Fill Task/Test IDs as work progresses.>
+
+## Persona Review Results
+
+| Persona | Status | Key Findings | Resolved |
+|---|---|---|---|
+| Requirements Engineer | PENDING | | |
+| Developer | PENDING | | |
+| Security | PENDING | | |
+| DevOps | PENDING | | |
+| UI/UX | PENDING | | |
+| Architect | PENDING | | |