fix(install): emit UTF-8 from skills_sync on non-UTF-8 Windows locales

On Windows with a non-UTF-8 system locale (e.g. CP936/GBK on zh-CN),
Python defaults stdout/stderr to the active codepage. tools/skills_sync.py
prints glyphs such as checkmark (U+2713) and up-arrow (U+2191) that GBK
cannot encode, raising UnicodeEncodeError mid-run.

The installer (scripts/install.ps1) captures this script's stdout and the
Rust bootstrap parses it as UTF-8 expecting a JSON result frame. A GBK
byte stream (or the traceback it triggers) surfaces as:

  WARN stdout read error: stream did not contain valid UTF-8
  stage=config-templates state=Failed
  error=install.ps1 -Stage config-templates produced no JSON result frame
        (exit=Some(0))

i.e. the stage fails even though the script exits 0. install.ps1 already
sets [Console]::OutputEncoding = UTF8, but that does not propagate to the
python.exe child (Python reads PYTHONIOENCODING / locale, not the console
encoding).

Fix in two places for defense in depth:
- tools/skills_sync.py: reconfigure sys.stdout/stderr to UTF-8 at import so
  output is valid UTF-8 regardless of caller or active codepage.
- scripts/install.ps1: set PYTHONIOENCODING=utf-8 and PYTHONUTF8=1 (scoped
  to the call, restored afterwards) around the skills_sync.py invocation.

scripts/install.ps1

@@ -2435,7 +2435,22 @@ You are Hermes Agent, an intelligent AI assistant created by Nous Research. You
     $pythonExe = "$InstallDir\venv\Scripts\python.exe"
     if (Test-Path $pythonExe) {
         try {
-            & $pythonExe "$InstallDir\tools\skills_sync.py" 2>$null
+            # Force the child python.exe to emit UTF-8 on its stdout/stderr.
+            # On non-UTF-8 Windows locales (CP936/GBK zh-CN) Python defaults
+            # its stream encoding to the active codepage and crashes on glyphs
+            # like ✓ (U+2713) that the codepage can't encode; the resulting
+            # non-UTF-8 bytes break this script's JSON result frame on stdout
+            # and abort the config-templates stage. Scope to this call only.
+            $prevPythonioencoding = $env:PYTHONIOENCODING
+            $prevPythonutf8 = $env:PYTHONUTF8
+            $env:PYTHONIOENCODING = "utf-8"
+            $env:PYTHONUTF8 = "1"
+            try {
+                & $pythonExe "$InstallDir\tools\skills_sync.py" 2>$null
+            } finally {
+                $env:PYTHONIOENCODING = $prevPythonioencoding
+                $env:PYTHONUTF8 = $prevPythonutf8
+            }
             Write-Success "Skills synced to $HermesHome\skills"
         } catch {
             # Fallback: simple directory copy