fix(notify): cross-platform TTY write with CONOUT$/CON fallback for Windows (fixes #15)

[MoerAI]

Summary

• Replace single /dev/tty write with a platform-aware cascade that works on Windows
• Port WARP_CLIENT_VERSION validation from claude-code-warp to skip broken Warp builds

Problem

warpNotify() writes OSC 777 via writeFileSync("/dev/tty"), which is Unix-only. On Windows, this silently fails and no notifications ever reach Warp. PR #12's process.stdout.write() fallback also doesn't work because OpenCode's plugin loader pipes stdout for RPC — it never reaches the terminal.

Additionally, some Warp builds set WARP_CLI_AGENT_PROTOCOL_VERSION without actually supporting structured notifications, causing the plugin to send events that are silently dropped.

Fix

src/notify.ts — New writeTty() function with ordered fallback:

1. /dev/tty — standard Unix controlling terminal (also works in WSL)
2. CONOUT$ — Windows console output device (bypasses stdio redirection)
3. CON — Windows console device (alternative path)
4. process.stderr — last resort, only if stderr is still a TTY

Each target is opened with openSync/writeSync/closeSync for proper fd management.

Added WARP_CLIENT_VERSION gating (ported from claude-code-warp's should-use-structured.sh) to avoid sending notifications to known-broken Warp builds.

Changes

File	Change
src/notify.ts	Replace writeFileSync("/dev/tty") with cross-platform writeTty() cascade; add WARP_CLIENT_VERSION check
tests/index.test.ts	Add writeTty smoke test

How to Test

1. On Windows: Install plugin locally, run opencode in Warp, send a query — notifications should appear
2. On macOS/Linux: Behavior unchanged (still uses /dev/tty first)

Fixes #15
Supersedes #12