Add gr-gsm and tshark as auto-installed dependencies

GSM Spy was failing with FileNotFoundError because grgsm_scanner
wasn't installed. These tools are now installed automatically by
setup.sh (both Debian and macOS) and included in the Dockerfile,
matching how other tools like multimon-ng and ffmpeg are handled.

- setup.sh: Remove ask_yes_no prompts for gr-gsm and tshark, install
  unconditionally; add check_recommended tier for final summary
- Dockerfile: Add tshark to apt layer, add gr-gsm RUN layer with
  apt-then-source-build fallback, preseed debconf for tshark
- gsm_spy.py: Add shutil.which pre-check in start_scanner route,
  catch FileNotFoundError in scanner_thread to stop retry loop

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

routes/gsm_spy.py

@@ -6,6 +6,7 @@ import json
 import logging
 import queue
 import re
+import shutil
 import subprocess
 import threading
 import time
@@ -361,6 +362,11 @@ def start_scanner():
 
         # Build grgsm_scanner command
         # Example: grgsm_scanner --args="rtl=0" -b GSM900
+        if not shutil.which('grgsm_scanner'):
+            from app import release_sdr_device
+            release_sdr_device(device_index)
+            return jsonify({'error': 'grgsm_scanner not found. Please install gr-gsm.'}), 500
+
         try:
             cmd = ['grgsm_scanner']
 
@@ -1325,6 +1331,22 @@ def scanner_thread(cmd, device_index):
 
                 logger.info(f"Scan #{scan_count} complete")
 
+            except FileNotFoundError:
+                logger.error(
+                    "grgsm_scanner not found. Please install gr-gsm: "
+                    "https://github.com/ptrkrysik/gr-gsm"
+                )
+                # Send error to SSE stream so the UI knows
+                try:
+                    app_module.gsm_spy_queue.put({
+                        'type': 'error',
+                        'message': 'grgsm_scanner not found. Please install gr-gsm.',
+                        'timestamp': time.strftime('%Y-%m-%dT%H:%M:%S')
+                    })
+                except Exception:
+                    pass
+                break  # Don't retry - binary won't appear
+
             except Exception as e:
                 logger.error(f"Scanner scan error: {e}", exc_info=True)
                 if process and process.poll() is None: