feat: add PTY_WEB_AUTOSTART environment variable support for V1 and V2 (#60)

[kumar-shivang]

Resolves #60

Motivation

As reported in #60, users running OpenCode (especially in V1 or via scripts configuring PTY_WEB_PORT) want to keep the Web UI open in a browser tab and view or interact with running PTY sessions without needing to wait or manually trigger /pty-open-background-spy or /pty-show-server-url.

In V1, the server was previously only instantiated on-demand when executing those slash commands. In V2, autostart was only configurable via ctx.options.autostart in opencode.json and did not inspect environment variables.

Summary of Changes

1. PTY_WEB_AUTOSTART Environment Variable:
   • Added PTYServer.isAutostartEnabled() helper supporting PTY_WEB_AUTOSTART and alias PTY_AUTOSTART (true, 1, yes, on).
2. OpenCode V1 Support (src/plugin.ts):
   • Automatically initializes and starts PTYServer during plugin setup if autostart is enabled.
   • Seamlessly reuses the already-running server instance when slash commands are invoked.
3. OpenCode V2 Support (src/v2/index.ts):
   • Falls back to PTYServer.isAutostartEnabled() when options.autostart is not explicitly provided in ctx.options.
   • Explicit options.autostart: false in config continues to take precedence over the environment variable.
4. Server Lifecycle Coordination:
   • Unified active server instance lifecycle management on PTYServer, delegating cleanly between V1 and V2.
5. Documentation:
   • Documented PTY_WEB_AUTOSTART in README.md under ### Environment Variables and updated the V2 options table.
6. Tests:
   • Added test/v1.test.ts verifying V1 autostart lifecycle and server reuse.
   • Added unit tests in test/v2.test.ts covering environment variable autostart and explicit config overrides.
   • All 89 tests pass across 17 test files with 0 lint/format/typecheck errors.