fix: add UTF-8 encoding for subprocess calls on Windows

On Windows, subprocess.Popen/run with text=True defaults to CP1252
encoding instead of UTF-8. This causes UnicodeDecodeError when
Claude outputs characters outside the CP1252 codepage.

Add explicit encoding="utf-8" and errors="replace" parameters to
all subprocess calls that use text=True.

Files modified:
- parallel_orchestrator.py (3 locations)
- start.py (2 locations)
- start_ui.py (1 location)

Closes #138

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cabana8471-arch

start.py

@@ -231,7 +231,9 @@ def run_spec_creation(project_dir: Path) -> bool:
             check=False,  # Don't raise on non-zero exit
             cwd=str(Path(__file__).parent),  # Run from project root
             stderr=subprocess.PIPE,
-            text=True
+            text=True,
+            encoding="utf-8",  # Fix Windows CP1252 encoding issue (#138)
+            errors="replace",
         )
 
         # Check for authentication errors in stderr
@@ -403,7 +405,9 @@ def run_agent(project_name: str, project_dir: Path) -> None:
             cmd,
             check=False,
             stderr=subprocess.PIPE,
-            text=True
+            text=True,
+            encoding="utf-8",  # Fix Windows CP1252 encoding issue (#138)
+            errors="replace",
         )
 
         # Check for authentication errors

start_ui.py

@@ -127,7 +127,9 @@ def check_node() -> bool:
         result = subprocess.run(
             ["node", "--version"],
             capture_output=True,
-            text=True
+            text=True,
+            encoding="utf-8",  # Fix Windows CP1252 encoding issue (#138)
+            errors="replace",
         )
         print(f"  Node.js version: {result.stdout.strip()}")
     except Exception: