feat: harden remote serve and reuse connections

- Gate TCP serve commands with safe-by-default policies, per-key allow tokens, per-key rate limiting, and audit labels.
- Reuse authenticated encrypted remote sessions and parallelize/caches multi-browser fanout to reduce repeated handshake roundtrips.
- Increase paged native-host batch size with extension-side byte budgeting to speed large tab listings safely.
- Point install output at public Chrome Web Store / Firefox AMO listings by default, with --dev preserving unpacked workflows.
- Share search-engine metadata between CLI and SDK and bump the package/extension version to 0.16.0.
- Cover the new security, pooling, paging, install, and fanout behavior with expanded Python and extension tests.

browser_cli/commands/install.py

@@ -10,7 +10,9 @@ from rich.console import Console
 
 from browser_cli.constants import (
   ALLOWED_EXTENSION_IDS,
+  CHROME_WEBSTORE_URL,
   EXTENSION_ID,
+  FIREFOX_ADDON_URL,
   FIREFOX_EXTENSION_ID,
   NATIVE_HOST_DIRS,
   NATIVE_HOST_NAME,
@@ -62,11 +64,44 @@ def _register_windows_native_host(browser: str, manifest_path: Path) -> list[str
 
 @click.command("install")
 @click.argument("browser", type=click.Choice(SUPPORTED_BROWSERS), default="chrome")
-def cmd_install(browser):
-  """Register the native messaging host and print extension load instructions."""
+@click.option("--dev", is_flag=True, help="Print developer instructions for loading an unpacked/temporary build instead of the public store listing.")
+def cmd_install(browser, dev):
+  """Register the native messaging host and print extension install instructions."""
   host_exe = native_host_exe()
   write_native_host_exe(host_exe)
 
+  if dev:
+    _print_dev_instructions(browser)
+  else:
+    _print_store_instructions(browser)
+
+  manifest = _native_host_manifest(browser, host_exe)
+  installed = _install_manifest(browser, host_exe, manifest)
+  if not installed:
+    console.print("[red]Failed to install native host manifest[/red]")
+    sys.exit(1)
+
+  for p in installed:
+    label = "Registered native host" if is_windows() else "Wrote native host manifest"
+    console.print(f"[green]✓[/green] {label}: {p}")
+  console.print(f"[green]✓[/green] Installed native host: {host_exe}")
+  console.print(f"\n[bold]Step 2:[/bold] Restart {browser.capitalize()} completely (quit app, then reopen)")
+  console.print("\n[green bold]✓ Installation complete![/green bold]")
+  console.print("  After restarting the browser, try: [cyan]browser-cli tabs list[/cyan]")
+
+def _print_store_instructions(browser: str) -> None:
+  console.print("\n[bold]Step 1:[/bold] Install the extension")
+  if browser == "firefox":
+    console.print("  Open Firefox Add-ons and click [bold]Add to Firefox[/bold]:")
+    console.print(f"  [cyan]{FIREFOX_ADDON_URL}[/cyan]")
+    console.print("  [dim]Firefox support is experimental; tab-group commands require browser tab group APIs.[/dim]\n")
+  else:
+    console.print(f"  Open the Chrome Web Store and click [bold]Add to {browser.capitalize()}[/bold]:")
+    console.print(f"  [cyan]{CHROME_WEBSTORE_URL}[/cyan]")
+    console.print("  [dim]Brave, Edge, Vivaldi and Chromium can install from the Chrome Web Store too.[/dim]")
+    console.print("  [dim]Developing the extension? Run 'browser-cli install <browser> --dev' for the unpacked-load steps.[/dim]\n")
+
+def _print_dev_instructions(browser: str) -> None:
   ext_url = {
     "chrome": "chrome://extensions",
     "chromium": "chrome://extensions",
@@ -75,7 +110,7 @@ def cmd_install(browser):
     "vivaldi": "vivaldi://extensions",
     "firefox": "about:debugging#/runtime/this-firefox",
   }[browser]
-  console.print("\n[bold]Step 1:[/bold] Load the extension in your browser")
+  console.print("\n[bold]Step 1:[/bold] Load the unpacked extension (developer mode)")
   console.print(f"  1. Open [cyan]{ext_url}[/cyan]")
   if browser == "firefox":
     repo_root = Path(__file__).parent.parent.parent
@@ -93,20 +128,6 @@ def cmd_install(browser):
     console.print(f"  4. Testing extension ID will be [cyan]{EXTENSION_ID}[/cyan] (fixed by built-in key)")
     console.print(f"     Chrome Web Store extension ID is [cyan]{WEBSTORE_EXTENSION_ID}[/cyan]\n")
 
-  manifest = _native_host_manifest(browser, host_exe)
-  installed = _install_manifest(browser, host_exe, manifest)
-  if not installed:
-    console.print("[red]Failed to install native host manifest[/red]")
-    sys.exit(1)
-
-  for p in installed:
-    label = "Registered native host" if is_windows() else "Wrote native host manifest"
-    console.print(f"[green]✓[/green] {label}: {p}")
-  console.print(f"[green]✓[/green] Installed native host: {host_exe}")
-  console.print(f"\n[bold]Step 2:[/bold] Restart {browser.capitalize()} completely (quit app, then reopen)")
-  console.print("\n[green bold]✓ Installation complete![/green bold]")
-  console.print("  After restarting the browser, try: [cyan]browser-cli tabs list[/cyan]")
-
 def _native_host_manifest(browser: str, host_exe: Path) -> dict:
   base = {
     "name": NATIVE_HOST_NAME,