feat(tools/zulip): chat bridge for projects whose primary chat is Zulip

Add `tools/zulip/` so skills can read chat context (and propose draft messages) where the project's primary chat is Zulip.

**Suggested capabilities:**

- `stream list` / `topic list ` / `message list `
- `search ` — message search across the org
- `user ` — profile, recent activity, role
- `message send --body-file ` — write (gated on explicit confirmation)
- `narrow ` — Zulip's filter DSL (powerful for "show me all messages by X in Y stream since Z")

**Why:** Zulip is primary chat for **Python core** (python.zulipchat.com), **Rust** (rust-lang.zulipchat.com), **Lean / mathlib** (a community-shaping move that drives lots of OSS interest), **Recurse Center**, **ZulipChat itself**, and a growing set of OSS projects. Its stream → topic → message hierarchy fits agentic chat-context lookup better than Slack/Discord — threads are first-class, not bolted on.

**Reference:**

- Zulip REST: https://zulip.com/api/rest
- Existing Slack integration shape (`mcp__claude_ai_Slack__*`) gives a reference for the chat-bridge surface shape — Zulip's threading model is cleaner, but the public-API contract is similar