Feat v0.6.15 user display audit

Add batch user resolve endpoint, sw.users SDK module, and migrate all
surfaces to show display_name instead of UUIDs. Canonical fallback chain:
display_name → username → "Unknown".

- GET /api/v1/users/resolve?ids=... (max 100, map response)
- sw.users.resolve(), resolveMany(), displayName() with 60s cache
- Chat participants resolved from users table, not snapshot
- Admin users/teams/groups/team-admin show display_name
- Chat-core participants.display_name column deprecated
- 5 new handler tests, OpenAPI spec updated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,41 @@
 
 All notable changes to Armature are documented here.
 
+## v0.6.15 — User Display Audit
+
+Every user-facing identity surface now shows human-readable names instead of
+UUIDs, with the canonical fallback chain: `display_name → username → "Unknown"`.
+
+### Added
+
+- **`GET /api/v1/users/resolve?ids=...`** — batch endpoint returns identity
+  records (username, display_name, handle, avatar_url) for up to 100 user IDs.
+  Response keyed by ID for O(1) client lookups.
+- **`sw.users` SDK module** — `resolve(id)`, `resolveMany(ids)`,
+  `displayName(user)` with 60-second local cache. Surfaces use this instead
+  of ad-hoc lookups or stale snapshots.
+- **5 handler tests** for the resolve endpoint (single, multiple, missing,
+  empty, no-param).
+
+### Changed
+
+- **Admin users list** — shows `display_name || username` as primary
+  identifier, with username shown as secondary when display_name is set.
+- **Admin teams/groups member lists** — replaced `username || user_id`
+  with `display_name || username || 'Unknown'`.
+- **Team-admin members** — dropdown and list now show display_name.
+- **Chat participants** — resolved from users table via `sw.users.resolveMany()`
+  instead of relying on creation-time snapshot. Message sender names, typing
+  indicators, and participant sidebar all use resolved names.
+- **Dashboard greeting** — added `|| 'Unknown'` terminal fallback.
+- **Team activity log** — capitalized fallback to `'Unknown'`.
+
+### Deprecated
+
+- **`participants.display_name` column** in chat-core — column retained for
+  backward compatibility but UI no longer relies on snapshot values. Comments
+  added to `packages/chat-core/script.star` noting deprecation.
+
 ## v0.6.14 — Visual Polish
 
 Systematic cleanup of stale values, self-hosted fonts, and rendering fixes.