test: cover gateway inbound filters and webhook bind edges

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Risky behavior now covered

• Discord drops bot authors and messages with no author, strips only a leading LICH_DISCORD_BOT_ID mention, and posts with allowed_mentions.parse empty so a reply cannot ping the room. A thrown handler becomes a one-line agent error and does not close the socket.
• Twitch does not answer its own nick, sends PASS oauth: once (no doubled prefix), drops a reply that sanitizes to empty, and strips a leading / before PRIVMSG.
• Telegram treats a non-array getUpdates result as no updates, skips bots and chat-less updates, keeps chat id 0, uses the media placeholder, and resets poll backoff to the first delay after a successful poll.
• Webhook bind allows only exact loopback names (127.0.0.1, localhost, ::1, including padding and case). Lookalikes ([::1], 127.1, ::ffff:127.0.0.1) stay refused, and the token is not logged. Non-object JSON is 400. Numeric chat and user ids are stringified. A chunked body over the byte cap, with no content-length, is 413 and never reaches the handler.

Test files added/updated

• Added test/gateway_inbound.test.ts
• Updated test/gateway.test.ts

Why this reduces regression risk

These are the chat-adapter and webhook edges from the gateway work (#174, #178) that the existing bus, reconnect, and policy tests do not hit. A regression here is a bot echo loop, a Twitch command sent from the bot, a mention ping, a public bind without a token, or an unbounded webhook body. Sleep and sockets are scripted, so the new cases do not wait on live network or the 2–30s backoff.

Validation

• node node_modules/vitest/vitest.mjs run test/gateway_inbound.test.ts test/gateway.test.ts — 49 passed
• node node_modules/typescript/bin/tsc --noEmit — passed
• Full suite not run; known environment failures remain when bun or dist/cli.js is missing.