fix: setup registration — use initDatabase/setRegisteredGroup, .ts imports, correct CLI commands

- setup/register.ts: replace inline DB logic with initDatabase() + setRegisteredGroup()
  (fixes missing is_main column on existing DBs, .js MODULE_NOT_FOUND with tsx)
- SKILL.md (telegram, slack, discord): replace broken registerGroup() pseudo-code
  with actual `npx tsx setup/index.ts --step register` commands
- docs/SPEC.md: fix registerGroup → setRegisteredGroup in example

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/add-slack/SKILL.md

@@ -114,31 +114,18 @@ Wait for the user to provide the channel ID.
 
 ### Register the channel
 
-Use the IPC register flow or register directly. The channel ID, name, and folder name are needed.
+The channel ID, name, and folder name are needed. Use `npx tsx setup/index.ts --step register` with the appropriate flags.
 
 For a main channel (responds to all messages):
 
-```typescript
-registerGroup("slack:<channel-id>", {
-  name: "<channel-name>",
-  folder: "slack_main",
-  trigger: `@${ASSISTANT_NAME}`,
-  added_at: new Date().toISOString(),
-  requiresTrigger: false,
-  isMain: true,
-});
+```bash
+npx tsx setup/index.ts --step register -- --jid "slack:<channel-id>" --name "<channel-name>" --folder "slack_main" --trigger "@${ASSISTANT_NAME}" --channel slack --no-trigger-required --is-main
 ```
 
 For additional channels (trigger-only):
 
-```typescript
-registerGroup("slack:<channel-id>", {
-  name: "<channel-name>",
-  folder: "slack_<channel-name>",
-  trigger: `@${ASSISTANT_NAME}`,
-  added_at: new Date().toISOString(),
-  requiresTrigger: true,
-});
+```bash
+npx tsx setup/index.ts --step register -- --jid "slack:<channel-id>" --name "<channel-name>" --folder "slack_<channel-name>" --trigger "@${ASSISTANT_NAME}" --channel slack
 ```
 
 ## Phase 5: Verify