add telegram channel worker with webhook and media support

[deathbyknowledge]

Summary

• add a new channels/telegram worker using Telegram Bot API webhooks + account Durable Object state
• wire Telegram into gateway bindings, CLI commands, deploy/bundle paths, alchemy wizard, and UI channel lists
• add outbound Telegram media support: single attachments and media groups (2-10) with URL/base64 inputs and caption handling
• update docs for Telegram setup/management and clarify that Telegram is webhook-driven (not always-on like WhatsApp/Discord)

Validation

• bunx tsc --noEmit -p channels/telegram/tsconfig.json
• bunx tsc --noEmit -p gateway/tsconfig.json
• bunx tsc --noEmit -p gateway/ui/tsconfig.json
• cargo check --manifest-path cli/Cargo.toml

[deathbyknowledge]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Configure Telegram webhook base URL during wizard deploy

In the Alchemy deployment path, the Telegram worker only receives TELEGRAM_BOT_TOKEN, so deployments created via gateway/alchemy never set TELEGRAM_WEBHOOK_BASE_URL. That breaks the post-deploy flow because TelegramChannel.start returns an error when this value is missing (channels/telegram/src/index.ts requires it before starting), despite the wizard step saying webhook setup is automatic. Users selecting Telegram in the wizard will hit a hard failure on gsv channel telegram start unless they manually inject the secret.

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