feat(conversation): CHAT-02 read-only Pi history reader and two board routes (#1507)

packages/conversation is a library with no server: safe-fs, the Pi session
parser, CHAT-01 pages, pinned snapshots, cursors and follow. The control
board adds GET /api/conversations and /api/conversation behind the Host
and Origin guard. Both are read-only, their queries are validated, and
each refusal code maps to a status.

Dewey authored it (packet 0cf177b1, revision 2). Filbert reviewed the code:
R1 revise (branch ids moving on append, the assumed-link bridge merging
branches, one unreadable seat directory turning the catalogue into a 500),
then R2 approve (3b14d66c). Darkwing reviewed the routes: R1 approve
(07b10ad1), R2 approve (b9d92003). The package lands with the routes,
because serve.mjs imports the reader at load.

On an index export: the eight suites 24/90/43/17/14/15/63/18,
conversation and control-board 153/153, webui 9/9.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/conversation/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "@mosaic/conversation",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Read-only Pi conversation histories for the Console: approved roots, safe opens, branch pages and cursors. No server; the control board serves it.",
+  "license": "UNLICENSED",
+  "type": "module",
+  "engines": { "node": ">=24" },
+  "exports": { ".": "./src/reader.mjs" },
+  "scripts": { "test": "node --test tests/" }
+}