fix(tools): remove dead code in _is_likely_binary and harden _check_lint against brace paths

- Remove unreachable `if not content_sample` branch inside the truthy
  `if content_sample` block in `_is_likely_binary()` (dead code that
  could never execute).
- Replace `linter_cmd.format(file=...)` with `linter_cmd.replace("{file}", ...)`
  in `_check_lint()` so file paths containing curly braces (e.g.
  `src/{test}.py`) no longer raise KeyError/ValueError.
- Add 16 unit tests covering both fixes and edge cases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tools/file_operations.py

@@ -386,9 +386,7 @@ class ShellFileOperations(FileOperations):
         
         # Content analysis: >30% non-printable chars = binary
         if content_sample:
-            if not content_sample:
-                return False
-            non_printable = sum(1 for c in content_sample[:1000] 
+            non_printable = sum(1 for c in content_sample[:1000]
                                if ord(c) < 32 and c not in '\n\r\t')
             return non_printable / min(len(content_sample), 1000) > 0.30
         
@@ -810,7 +808,7 @@ class ShellFileOperations(FileOperations):
             return LintResult(skipped=True, message=f"{base_cmd} not available")
         
         # Run linter
-        cmd = linter_cmd.format(file=self._escape_shell_arg(path))
+        cmd = linter_cmd.replace("{file}", self._escape_shell_arg(path))
         result = self._exec(cmd, timeout=30)
         
         return LintResult(