Fix UTF-8 decoding error when verifying signatures with international characters

Issue: GPG verification crashed with UnicodeDecodeError when signatures
contained international characters (German ö, Turkish ü, etc.) in the
signed content.

Error: "'utf-8' codec can't decode byte 0xf6 in position 160"

Root cause: subprocess.Popen was using default text decoding without
handling encoding errors gracefully.

Solution:
1. Changed LC_ALL/LANG from 'C' to 'C.UTF-8' to ensure GPG uses UTF-8
2. Added explicit encoding='utf-8' parameter to Popen
3. Added errors='replace' to replace invalid UTF-8 bytes instead of crashing

This allows the verification to proceed even if GPG's output contains
characters that don't decode cleanly, ensuring robustness with
multilingual content.

trace/crypto.py

@@ -46,8 +46,8 @@ class Crypto:
             # Force English output for consistent parsing across locales
             import os
             env = os.environ.copy()
-            env['LC_ALL'] = 'C'
+            env['LC_ALL'] = 'C.UTF-8'  # Use UTF-8 variant to handle international characters
-            env['LANG'] = 'C'
+            env['LANG'] = 'C.UTF-8'
 
             proc = subprocess.Popen(
                 ['gpg', '--verify'],
@@ -55,6 +55,8 @@ class Crypto:
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
                 text=True,
+                encoding='utf-8',
+                errors='replace',  # Replace invalid UTF-8 sequences instead of crashing
                 env=env
             )
             stdout, stderr = proc.communicate(input=signed_content, timeout=10)