feat(discord): connector pilot for the Sage seat, reviewed candidate (#1509)

Zero-dependency Discord connector under packages/discord: binding
validation, REST and gateway clients, pi engine adapter, journal with
append-only inbox, outbox, admissions and notices, and a run.lock
ownership record {pid, start, boot} whose identity is checked three ways
and whose cleanup is gated by STOP. CLI check|run|stop|unlock via
scripts/discord.sh; offline suite scripts/test-discord.sh (28 checks,
87 node tests).

Reviewed by rev-code-02 on #1509 over nine rounds; approved exact tree
4e0feb6758c0a7e4a71483912a8e0d3e3ec95aef at comment 26170. Corrections
(1) to (12) recorded in BUILD-LOG. No listener started, no token read,
no Discord write; the live pilot follows this commit per the brief.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

packages/discord/fixtures/binding.example.json

@@ -0,0 +1,31 @@
+{
+  "bindingVersion": 1,
+  "name": "example-seat",
+  "seat": "sage",
+  "guildId": "100000000000000001",
+  "guildName": "Example Server",
+  "botUserId": "100000000000000002",
+  "tokenFile": "/home/example/secrets/discord-example.token",
+  "channels": [
+    { "id": "100000000000000010", "name": "seat-admin", "mode": "open" },
+    { "id": "100000000000000011", "name": "general", "mode": "mention" }
+  ],
+  "users": [
+    { "id": "100000000000000100", "name": "owner" }
+  ],
+  "engine": { "provider": "zai", "model": "glm-5.3", "thinking": "high" },
+  "limits": {
+    "turnsPerDay": 200,
+    "turnTimeoutSeconds": 180,
+    "replyChunkChars": 1900,
+    "inboundMaxChars": 4000
+  },
+  "context": {
+    "files": [
+      "contracts/CONSTITUTION.md",
+      "contracts/STANDARDS.md",
+      "agents/sage/SOUL.md",
+      "agents/sage/DISCORD-USER.md"
+    ]
+  }
+}