When running capa with Binary Ninja backend, Binja not found

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### Description

When running capa against shellcode using the Binary Ninja backend, capa indicates the Binary Ninja API is not found.
Mentioning @xusheng6 since I believe he works issues related to Binja. Thank you!

### Steps to Reproduce

Run capa on shellcode using Binary Ninja as a backend with the following command:
`C:\Tools\capa.exe -r C:\Tools\capa-rules -f sc64 sc.bin -b binja -d`

**Expected behavior:**
capa should analyze the shellcode file with the binary ninja backend and report any detected capabilities based on the specified rules.

**Actual behavior:**
The above command produces the following error:
```
DEBUG capa: using rules path: C:\Tools\capa-rules main.py:495
DEBUG capa.rules: reading rules from directory C:\Tools\capa-rules __init__.py:2101
DEBUG capa.rules.cache: loading rule set from cache: C:\Users\REM\AppData\Local\flare\capa\cache\capa-6b587440.cache cache.py:150
DEBUG capa: successfully loaded 969 rules main.py:683
DEBUG capa.features.extractors.common: unsupported file format: fc4883e4, will not guess OS common.py:141
DEBUG capa: skipping library code matching: only supported by the vivisect backend main.py:783
DEBUG capa: format: sc64 main.py:833
DEBUG capa: backend: binja main.py:834
DEBUG capa.features.extractors.binja.find_binja_api: Binary Ninja API not installed, searching... find_binja_api.py:149
WARNING capa.features.extractors.binja.find_binja_api: unsupported platform to find Binary Ninja: win32 find_binja_api.py:110
DEBUG capa.features.extractors.binja.find_binja_api: failed to find Binary Ninja installation find_binja_api.py:153
DEBUG capa.features.extractors.binja.find_binja_api: found Binary Ninja API: None find_binja_api.py:155
Traceback (most recent call last):
File "main.py", line 1103, in
File "main.py", line 990, in main
File "main.py", line 837, in get_extractor_from_cli
File "loader.py", line 246, in get_extractor
RuntimeError: cannot find Binary Ninja API module.
[PYI-4732:ERROR] Failed to execute script 'main' due to unhandled exception!
```

### Versions
capa version: 8.0.1
capa rules version: 8.0.1
Installed as: Tried both Python library and standalone EXE
Backend: Binary Ninja 4.2.6455 (Personal License)

### Additional Information
- I installed the Binary Ninja API as described here: https://docs.binary.ninja/dev/batch.html#install-the-api.
- I manually executed `python find_binja_api.py` (the file referenced in the debug output), and it outputs the path `C:\Users\REM\AppData\Local\Programs\Vector35\BinaryNinja\python`.
- I also ran this code, located in `find_binja_api.py`, with the following output:
```
>>> import importlib.util
>>> importlib.util.find_spec("binaryninja")
ModuleSpec(name='binaryninja', loader=<_frozen_importlib_external.SourceFileLoader object at 0x000001F77ABE8350>, origin='C:\\Users\\REM\\AppData\\Local\\Programs\\Vector35\\BinaryNinja\\python\\binaryninja\\__init__.py', submodule_search_locations=['C:\\Users\\REM\\AppData\\Local\\Programs\\Vector35\\BinaryNinja\\python\\binaryninja'])
```

Any ideas are much appreciated. Thank you!

Start with find_binja_api.py and reproduce the reported Windows command using the Binary Ninja backend. Compare its API discovery behavior with the documented installation and the successful importlib.util.find_spec("binaryninja") result. Done means capa can locate the Binary Ninja API and analyze the shellcode without the RuntimeError.

Written by the indexing model from the issue text.