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/features/_example/adr-001-avatars-reuse-archive-bucket.md

@@ -0,0 +1,46 @@
+# ADR-001 (feature-local) — Avatars reuse the archive bucket under an `avatars/` prefix
+
+**Status:** Accepted
+**Date:** 2026-06-13
+**Issue:** #<example> (profile picture upload)
+
+> **Feature-local ADR.** This decision is scoped to the avatar feature and lives with its
+> spec. A decision with project-wide reach is promoted to the permanent archive at
+> `docs/adr/` with the next free number. (For the worked example, it stays local.)
+
+## Context
+
+Avatars are small binary objects keyed per user. The project already runs MinIO with a
+single archive bucket and a `FileService` abstraction used by document uploads. We must
+decide where avatar bytes live without adding operational surface that the self-hosted
+Compose deployment has to learn about.
+
+## Decision
+
+Store each avatar in the **existing archive bucket** under the deterministic key
+`avatars/{userId}`, written and read through the existing `FileService`. No new bucket, no
+new env var, no new Compose service or bucket-bootstrap step.
+
+## Alternatives Considered
+
+| Option | Pros | Cons | Reason rejected |
+|---|---|---|---|
+| Reuse archive bucket, `avatars/` prefix | No infra change; reuses `FileService`; idempotent overwrite | Mixes avatars with documents in one bucket | **Chosen** — least operational cost; prefix keeps them logically separate |
+| Dedicated `avatars` bucket | Clean separation; independent lifecycle/policy | New bucket + bootstrap step + env var + Compose idempotency test | Operational overhead not justified for small, low-value objects |
+| Store bytes in PostgreSQL (`bytea`) | One datastore; transactional with the row | Bloats the DB and backups; streaming images via JPA is awkward | Wrong tool; MinIO already exists for blobs |
+| External CDN / object store | Offloads bandwidth | New third-party dependency + secret + ADR; conflicts with self-hosted goal | Contradicts the self-hosted infrastructure stance |
+
+## Consequences
+
+- No deployment change ships with this feature — only a Flyway column and code.
+- Avatars and documents share a bucket; any future per-object lifecycle policy must filter
+  by the `avatars/` prefix.
+- The deterministic key (`avatars/{userId}`, no random suffix) makes replace an overwrite,
+  so there is no orphan-cleanup obligation (REQ-001).
+- If avatars later need independent retention or a public CDN, this ADR is superseded by a
+  project-wide ADR in `docs/adr/`.
+
+## References
+
+- [`./spec.md`](./spec.md), [`./design.md`](./design.md)
+- [constitution §5 Dependency Policy](../../constitution.md#5-dependency-policy)