Feat v0.5.1 chat core (#31)

Co-authored-by: Jeffrey Smith <jasafpro@gmail.com>
Co-committed-by: Jeffrey Smith <jasafpro@gmail.com>

CHANGELOG.md

@@ -2,6 +2,46 @@
 
 All notable changes to Switchboard Core are documented here.
 
+## v0.5.1 — Chat Core Library
+
+### Added
+
+- **`chat-core` library package**: Conversations, messages, participants, and
+  read cursors as ext_data tables. Permissions: `db.write`, `realtime.publish`.
+  Consumable by other packages via `lib.require("chat-core")`.
+- **4 ext_data tables**: `conversations` (title, type, created_by, updated_at),
+  `participants` (conversation_id, participant_id, type, display_name, role,
+  joined_at), `messages` (conversation_id, participant_id, content, content_type,
+  edited_at), `read_cursors` (conversation_id, participant_id,
+  last_read_message_id).
+- **6 exported Starlark functions**: `create()`, `send()`, `history()`,
+  `add_participant()`, `remove_participant()`, `mark_read()`.
+- **15 REST endpoints**: Full CRUD for conversations, messages, participants.
+  Cursor-based paginated message history. Per-conversation unread counts.
+- **Realtime events**: `message`, `message.edited`, `message.deleted`,
+  `participant.added`, `participant.removed` published to
+  `conversation:{id}` channels.
+- **`db.query()` range parameters**: New `before` and `after` kwargs accept
+  dicts of `{col: val}` generating `col < ?` / `col > ?` WHERE clauses.
+  Enables cursor-based pagination and efficient unread counting for all
+  extension packages. 7 new Go tests.
+
+### Security
+
+- **Invisible Unicode scanning gate** (GlassWorm / Trojan Source defense):
+  `ScanSource()` detects variation selectors, bidi overrides, zero-width chars,
+  tag characters, and other invisible Unicode across 10 ranges. `Verdict()`
+  blocks GlassWorm payloads (>=10 variation selector / tag chars), Trojan Source
+  (any bidi override), and excessive zero-width chars (>=6). Two enforcement
+  points: extension install (422 rejection before files written) and Starlark
+  execution (belt-and-suspenders). 23 new tests including GlassWorm payload
+  simulation.
+
+### Changed
+
+- **Admin packages type filter**: Added `Library` option alongside Surface/Extension/Full/Workflow. Filter dropdown replaced button group with themed `Dropdown` primitive (keyboard nav, CSS-var theming, consistent with rest of admin UI).
+- SDK version bumped from 0.5.0 to 0.5.1.
+
 ## v0.5.0 — Realtime Primitive + Dialog Audit + Permissions UI
 
 ### Added