fix(windows): use PortableGit (not MinGit), fix relaunch os.execvp crash, surface npm errors

Three real bugs from teknium1's first Windows install run:

1. **MinGit has no bash.exe.**  MinGit is the minimal-automation Git for Windows
   distribution — it ships git.exe but deliberately strips bash and the POSIX
   coreutils.  Installer logged "Could not locate bash.exe" and Hermes would
   fail to run any shell command.  Switched to PortableGit — the full Git for
   Windows minus the installer UI.  PortableGit ships bash.exe at
   <root>\bin\bash.exe plus sh, awk, sed, grep, curl, ssh in usr\bin\.  ARM64
   variant is detected separately (PortableGit-*-arm64.7z.exe).  32-bit falls
   back to MinGit-32-bit with a warning (PortableGit is 64-bit only).

   PortableGit ships as a 7z self-extractor (56MB vs MinGit's 38MB).  We
   invoke it with `-o<target> -y` to extract silently — no 7z install needed,
   it's self-contained.

   Updated tools/environments/local.py::_find_bash candidate order to prefer
   the PortableGit layout (<root>\bin\bash.exe) with the MinGit layout
   (<root>\usr\bin\bash.exe) as a fallback so existing installs keep working.

2. **os.execvp "Exec format error" on Windows.**  Setup wizard's "Launch
   hermes chat now? Y" called `os.execvp(["hermes", "chat"])` which on
   Windows can only swap to real Win32 .exe files — chokes with OSError(8)
   on .cmd batch shims and Python console-script wrappers.  Added a
   win32 branch in hermes_cli/relaunch.py::relaunch() that uses
   subprocess.run + sys.exit — functionally identical (user sees "hermes
   exited, then new hermes started") with one extra PID in play.  POSIX
   path is UNCHANGED — still uses os.execvp for in-place replacement.
   Catches OSError in the Windows branch and surfaces a "open a new
   terminal so PATH picks up, then re-run hermes" hint instead of a
   cryptic traceback.

3. **npm install failures silent on Windows.**  The install.ps1 was invoking
   `npm install --silent 2>&1 | Out-Null` inside a try/catch.  PowerShell's
   try/catch does NOT trigger on non-zero process exit codes — only on
   unhandled .NET exceptions — so npm failing printed a generic "npm
   install failed" with zero information about WHY.  The silent pipe ate
   the stderr.

   Rewrote Install-NodeDeps to:
   - Resolve npm.cmd via Get-Command (respects PATHEXT) instead of
     relying on bare `npm` name resolution.
   - Use Start-Process with -PassThru to capture the actual exit code.
   - Redirect stderr to a temp log and surface the first ~800 chars of
     the real npm error when install fails, plus the log path for the
     full text.
   - Fail loudly with the right exit code instead of a misleading success.
   - Bail cleanly with a helpful message when npm isn't on PATH at all.

4. **"True" printing to console after Node check.**  `Test-Node` returns $true;
   installer called it as a bare statement (no assignment, no cast).  PowerShell
   prints bare return values.  Wrapped the call in `[void](Test-Node)`.

## Tests

- Added 3 new tests in tests/hermes_cli/test_relaunch.py covering the
  Windows branch: subprocess is called (not execvp), child exit code
  propagates, OSError surfaces a helpful message.  All 23 tests pass
  (20 existing + 3 new).
- 77 Windows-compat tests still pass, POSIX behaviour unchanged.

tools/environments/local.py

@@ -190,16 +190,21 @@ def _find_bash() -> str:
     if custom and os.path.isfile(custom):
         return custom
 
-    # Prefer our own portable MinGit install first — this way a broken or
+    # Prefer our own portable Git install first — this way a broken or
     # partially-uninstalled system Git can't hijack the bash lookup.  The
-    # install.ps1 installer always drops MinGit here when the user didn't
-    # already have a working system Git.
+    # install.ps1 installer always drops portable Git here when the user
+    # didn't already have a working system Git.
+    #
+    # Layouts (both checked so upgrades between MinGit and PortableGit
+    # installs work transparently):
+    #   PortableGit: %LOCALAPPDATA%\hermes\git\bin\bash.exe   (primary)
+    #   MinGit:      %LOCALAPPDATA%\hermes\git\usr\bin\bash.exe (legacy/32-bit fallback)
     _local_appdata = os.environ.get("LOCALAPPDATA", "")
     _hermes_portable_git = os.path.join(_local_appdata, "hermes", "git") if _local_appdata else ""
     if _hermes_portable_git:
         for candidate in (
-            os.path.join(_hermes_portable_git, "usr", "bin", "bash.exe"),  # MinGit layout
-            os.path.join(_hermes_portable_git, "bin", "bash.exe"),         # non-MinGit portable
+            os.path.join(_hermes_portable_git, "bin", "bash.exe"),        # PortableGit (primary)
+            os.path.join(_hermes_portable_git, "usr", "bin", "bash.exe"), # MinGit fallback
         ):
             if os.path.isfile(candidate):
                 return candidate