feat: native Windows support for browse tool

[fqueiro]

Summary

• Add native Windows support for the gstack browse tool (headless Chromium server + CLI)
• On Windows, Bun's subprocess/pipe handling breaks Playwright's CDP connection, so the browse server runs under Node+tsx via a new server-node.mjs entry point
• Cross-platform platform.ts module replaces all hardcoded /tmp paths, startsWith('/') checks, and dir + '/' path comparisons with OS-aware equivalents
• Cookie import correctly gated to macOS-only (requires Keychain access)

Key changes

• browse/src/platform.ts — new shared module: IS_WINDOWS, IS_MACOS, TEMP_DIR, getSafeDirectories(), isPathWithin()
• browse/src/server-node.mjs — Node-compatible server entry point for Windows with Bun API shim (Bun.which, Bun.sleep)
• browse/src/server-shared.ts — extracted generateHelpText(), wrapError(), dispatchCommand() shared between Bun and Node servers
• browse/src/cli.ts — Windows: resolve .cmd shim to real bun.exe, use child_process.spawn with detached:true, use node --import tsx for server
• browse/src/config.ts — replace Bun.spawnSync with Node spawnSync for git commands
• browse/src/cookie-import-browser.ts — dynamic bun:sqlite import, macOS-only guards, async listDomains()
• browse/src/find-browse.ts — look for browse.exe on Windows
• browse/src/meta-commands.ts, read-commands.ts, snapshot.ts, write-commands.ts — use platform.ts for safe paths
• package.json — add tsx devDependency for Windows Node server

Test plan

• 25 new tests: platform.test.ts (12) + server-shared.test.ts (13) — all pass on Windows, platform-agnostic
• Existing cookie-import-browser.test.ts updated for async listDomains() — passes
• find-browse.test.ts — passes (finds browse.exe)
• Manual: verify $B goto <url> works end-to-end on Windows — ✅ tested: server starts, navigates, screenshots, snapshots with refs all work
• Manual: verify browse tool still works on macOS (no regressions) — needs maintainer verification (I don't have access to a Mac)

🤖 Generated with Claude Code

[garrytan]

Closed in favor of #255 (v0.9.3.0). Your platform.ts module and cross-platform path handling were great — we adopted the same pattern. The Node.js fallback approach from #194 was more minimal for the server side. Thanks @fqueiro for the comprehensive work and tests!

[garrytan]

Thank you @fqueiro! Your identification of child_process.spawn({ detached: true }) as the correct Windows detachment approach was exactly right — we've credited this in #431's commit message and PR body. The fix in #431 builds on this insight along with the Node.js server fallback from #255. Closing in favor of #431.