refactor(v2): move channel adapters off v2 trunk

v2 ships with no channels baked in. All channel adapters (discord, slack,
telegram + helpers, whatsapp, whatsapp-cloud, gchat, github, imessage,
linear, matrix, resend, teams, webex) and their channel-specific setup
steps (pair-telegram, whatsapp-auth) now live on the `channels` branch
and get copied in via /add-*-v2 skills.

Removed:
- src/channels/{discord,slack,telegram*,whatsapp*,gchat,github,imessage,linear,matrix,resend,teams,webex}.ts
- setup/{pair-telegram,whatsapp-auth}.ts
- 14 channel-specific deps from package.json (@chat-adapter/*, @beeper/*,
  @bitbasti/*, @resend/chat-sdk-adapter, @whiskeysockets/baileys,
  chat-adapter-imessage, qrcode, @chat-adapter/state-memory unused)
- Their corresponding STEPS entries from setup/index.ts
- Channel imports from src/channels/index.ts

Kept:
- Channel infra: adapter.ts, channel-registry.ts (+ test), chat-sdk-bridge.ts,
  ask-question.ts, an empty-imports index.ts
- Chat SDK runtime (`chat`) for channels that copy in via Chat SDK bridge
- @chat-adapter/shared promoted from transitive to direct dep
  (channel-registry.ts uses NetworkError from it)

Verified: pnpm run build clean, 326 host tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

setup/pair-telegram.ts

@@ -1,116 +0,0 @@
-/**
- * Step: pair-telegram — issue a one-time pairing code and wait for the
- * operator to send `@botname CODE` from the chat they want to register.
- *
- * On success, prints platformId / isGroup / pairedUserId / intent. The caller
- * (skill) can then wire the chat to an agent group (e.g. via /init-first-agent
- * or setup --step register). telegram.ts's inbound interceptor has already
- * upserted the paired user and granted owner if no owner existed yet.
- *
- * The service must already be running so the telegram adapter is polling.
- */
-import { initDb } from '../src/db/connection.js';
-import { runMigrations } from '../src/db/migrations/index.js';
-import { DATA_DIR } from '../src/config.js';
-import path from 'path';
-
-import {
-  createPairing,
-  waitForPairing,
-  type PairingIntent,
-} from '../src/channels/telegram-pairing.js';
-import { emitStatus } from './status.js';
-
-function parseArgs(args: string[]): PairingIntent {
-  let intent: PairingIntent = 'main';
-  for (let i = 0; i < args.length; i++) {
-    switch (args[i]) {
-      case '--intent': {
-        const raw = args[++i] || 'main';
-        if (raw === 'main') {
-          intent = 'main';
-        } else if (raw.startsWith('wire-to:')) {
-          intent = { kind: 'wire-to', folder: raw.slice('wire-to:'.length) };
-        } else if (raw.startsWith('new-agent:')) {
-          intent = { kind: 'new-agent', folder: raw.slice('new-agent:'.length) };
-        } else {
-          throw new Error(`Unknown intent: ${raw}`);
-        }
-        break;
-      }
-    }
-  }
-  return intent;
-}
-
-function intentToString(intent: PairingIntent): string {
-  if (intent === 'main') return 'main';
-  return `${intent.kind}:${intent.folder}`;
-}
-
-export async function run(args: string[]): Promise<void> {
-  const intent = parseArgs(args);
-
-  // Pairing reads/writes its JSON store under DATA_DIR; the DB isn't strictly
-  // required for the pairing primitive itself, but the inbound interceptor
-  // (running in the live service) needs it. Touch it here so a fresh install
-  // doesn't blow up on the first match.
-  const db = initDb(path.join(DATA_DIR, 'v2.db'));
-  runMigrations(db);
-
-  const MAX_REGENERATIONS = 5;
-  let record = await createPairing(intent);
-  emitStatus('PAIR_TELEGRAM_ISSUED', {
-    CODE: record.code,
-    INTENT: intentToString(intent),
-    INSTRUCTIONS: `Send "${record.code}" from the Telegram chat you want to register (or "@<botname> ${record.code}" in a group with privacy on).`,
-    REMINDER_TO_ASSISTANT: `Your next user-visible message MUST include this CODE in plain text — the bash tool output this block is in gets collapsed in the UI.`,
-  });
-
-  for (let regen = 0; regen <= MAX_REGENERATIONS; regen++) {
-    try {
-      const consumed = await waitForPairing(record.code, {
-        onAttempt: (a) => {
-          emitStatus('PAIR_TELEGRAM_ATTEMPT', {
-            EXPECTED_CODE: record.code,
-            RECEIVED_CODE: a.candidate,
-            PLATFORM_ID: a.platformId,
-            AT: a.at,
-          });
-        },
-      });
-      emitStatus('PAIR_TELEGRAM', {
-        STATUS: 'success',
-        CODE: record.code,
-        INTENT: intentToString(consumed.intent),
-        PLATFORM_ID: consumed.consumed!.platformId,
-        IS_GROUP: consumed.consumed!.isGroup,
-        PAIRED_USER_ID: consumed.consumed!.adminUserId
-          ? `telegram:${consumed.consumed!.adminUserId}`
-          : '',
-      });
-      return;
-    } catch (err) {
-      const message = err instanceof Error ? err.message : String(err);
-      const invalidated = /invalidated by wrong code/.test(message);
-      if (invalidated && regen < MAX_REGENERATIONS) {
-        record = await createPairing(intent);
-        emitStatus('PAIR_TELEGRAM_NEW_CODE', {
-          CODE: record.code,
-          INTENT: intentToString(intent),
-          REASON: 'previous code invalidated by wrong attempt',
-          REGENERATIONS_LEFT: MAX_REGENERATIONS - regen - 1,
-          INSTRUCTIONS: `Send "${record.code}" from the Telegram chat you want to register.`,
-          REMINDER_TO_ASSISTANT: `Your next user-visible message MUST include this CODE in plain text — the bash tool output this block is in gets collapsed in the UI.`,
-        });
-        continue;
-      }
-      emitStatus('PAIR_TELEGRAM', {
-        STATUS: 'failed',
-        CODE: record.code,
-        ERROR: invalidated ? 'max-regenerations-exceeded' : message,
-      });
-      process.exit(2);
-    }
-  }
-}