Linux support for the external Python client

[pskeshu]

Follow-up to #1. That PR made the desktop app build and run on Linux; this one
makes the external Python API (ScopeOneCore/python/scopeone) work there too,
so a running ScopeOne can be driven from Python on Linux. Windows behaviour is
unchanged — every platform-specific path is guarded by _WIN32 (C++) or
os.name (Python).

The control protocol (length-prefixed JSON) and the shared-frame layout are
already platform-neutral; only the two transports were Windows-only.

What's in this PR (4 files)

Control channel — src/ScopeOneLocalApiServer.cpp

• The server name was the literal Windows pipe string, which QLocalServer drops
  verbatim into a socket path on Unix. Made it platform-aware: keep the named
  pipe on Windows, use a plain ScopeOne.Api.local name on Unix (Qt resolves it
  to a unix socket under the temp dir).

Frame export — src/ScopeOneLocalApiServer.cpp / .h

• On Windows the local-API frame block is a named file mapping
  (CreateFileMapping) that the client opens by name. This adds the Linux
  equivalent: a POSIX shared-memory object (shm_open + mmap) at
  /dev/shm/ScopeOne.Api.frame, cleaned up with munmap/shm_unlink on
  shutdown.

Python client — ScopeOneCore/python/scopeone

• Split the transport behind one internal interface: Windows keeps the pywin32
  named pipe + mmap(tagname=...); Linux uses an AF_UNIX socket and reads
  frames by mmap-ing the /dev/shm object. The public API, the request
  protocol, and shm.py are unchanged.
• pyproject.toml: pywin32 is now a Windows-only dependency, and the Linux
  classifier is added.

Verification

Tested end-to-end against the demo camera on Linux (Manjaro, Qt 6.11, Python
3.14):

connect -> load_config -> start_preview -> record(3) -> session.frame("Camera", 0)
=> (512, 512) uint16 numpy array

No extra Python dependencies on Linux — the client uses only the standard
library (socket, mmap).

Scope

• Demo camera; Windows transports unchanged (guarded, not re-tested on my end —
  a Windows check would be welcome).
• No other behaviour touched.