CI(windows): force UTF-8 stdio so hf download / Studio CLI don't crash on Windows

Windows defaults to cp1252 ("charmap"); the hf-hub CLI prints a
success checkmark "✓" (U+2713) and the bare hf download in the
"Prime HF_HOME" step dies with:

  Error: Invalid value. 'charmap' codec can't encode character
  '✓' in position 5: character maps to <undefined>

Set PYTHONIOENCODING=utf-8 and PYTHONUTF8=1 at the job level for all
four Windows Studio workflows. Same env vars work on Linux/Mac as
no-ops, so we don't need OS-conditional handling.

.github/workflows/studio-windows-api-smoke.yml

@@ -46,6 +46,10 @@ jobs:
       GGUF_FILE: gemma-3-270m-it-UD-Q4_K_XL.gguf
       STUDIO_PORT: '18895'
       HF_HOME: ${{ github.workspace }}/hf-cache
+      # Force UTF-8 for stdio (Windows defaults to cp1252; hf
+      # download prints a "✓" checkmark and crashes otherwise).
+      PYTHONIOENCODING: utf-8
+      PYTHONUTF8: '1'
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
 

.github/workflows/studio-windows-inference-smoke.yml

@@ -55,6 +55,11 @@ jobs:
       GGUF_FILE: gemma-3-270m-it-UD-Q4_K_XL.gguf
       STUDIO_PORT: '18888'
       HF_HOME: ${{ github.workspace }}/hf-cache
+      # Force UTF-8 for stdio (Windows defaults to cp1252; hf
+      # download / Studio CLI print "✓" checkmarks and crash
+      # otherwise).
+      PYTHONIOENCODING: utf-8
+      PYTHONUTF8: '1'
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
 
@@ -271,6 +276,11 @@ jobs:
       GGUF_FILE: Qwen3.5-2B-UD-Q4_K_XL.gguf
       STUDIO_PORT: '18898'
       HF_HOME: ${{ github.workspace }}/hf-cache
+      # Force UTF-8 for stdio (Windows defaults to cp1252; hf
+      # download / Studio CLI print "✓" checkmarks and crash
+      # otherwise).
+      PYTHONIOENCODING: utf-8
+      PYTHONUTF8: '1'
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
 
@@ -576,6 +586,11 @@ jobs:
       MMPROJ_FILE: mmproj-F16.gguf
       STUDIO_PORT: '18899'
       HF_HOME: ${{ github.workspace }}/hf-cache
+      # Force UTF-8 for stdio (Windows defaults to cp1252; hf
+      # download / Studio CLI print "✓" checkmarks and crash
+      # otherwise).
+      PYTHONIOENCODING: utf-8
+      PYTHONUTF8: '1'
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
 

.github/workflows/studio-windows-ui-smoke.yml

@@ -49,6 +49,12 @@ jobs:
       GGUF_FILE: gemma-3-270m-it-UD-Q4_K_XL.gguf
       STUDIO_PORT: '18896'
       HF_HOME: ${{ github.workspace }}/hf-cache
+      # Force UTF-8 for stdio so Python tools (hf download, Studio
+      # CLI, etc.) can print Unicode characters like the success
+      # checkmark "✓". Windows defaults to cp1252 / charmap and
+      # any tool that prints "OK ✓" hits a UnicodeEncodeError.
+      PYTHONIOENCODING: utf-8
+      PYTHONUTF8: '1'
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
 

.github/workflows/studio-windows-update-smoke.yml

@@ -50,6 +50,12 @@ jobs:
     defaults:
       run:
         shell: bash
+    env:
+      # Force UTF-8 for stdio (Windows defaults to cp1252; hf
+      # download / Studio CLI print "✓" checkmarks and crash
+      # otherwise).
+      PYTHONIOENCODING: utf-8
+      PYTHONUTF8: '1'
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1