fix: threaded HTTP server so the RAM modal progress is live (v3.6.39)

__main__ built a plain HTTPServer (single-threaded): during a RAM install
POST every other request waited in the accept queue, including the 2 s
/api/status poll that feeds the operation modal - its bar and step
headline never moved and the whole result appeared only at the end (live
2026-09-29).

_build_http_server() now returns a ThreadingHTTPServer (daemon threads).
Card access is unchanged: it is serialized by _CARD_LOCK, not by the
server - every POST is blanket-wrapped in do_POST, every /api/ GET except
/api/status and /api/test/status is wrapped in do_GET, and the background
threads (STATUS poll, _bip_data_available, test runner) take the lock;
the audit found no card-access holes.  do_GET also lets non-/api (static
PWA) paths bypass the lock, so page assets stay answerable during long
operations.

Regression test tests/test_http_concurrency.py: a fast request must
complete while a slow one is in flight (fails on HTTPServer with exactly
the reported symptom: 1.01 s vs 0.20 s); test_startup_cardless patches
the new factory.

sw cache simple-v312; tests: 519 Python / 674 Node.

pysim_simple_server/server.py

@@ -31,7 +31,7 @@ from osmocom.tlv import BER_TLV_IE
 from osmocom.utils import rpad
 
 
-VERSION = '3.6.38'
+VERSION = '3.6.39'
 
 MAX_ENVELOPE_SEGMENTS = 5  # max SMS segments for outgoing C-APDU in ENVELOPE
 
@@ -5328,7 +5328,11 @@ class PysimHandler(BaseHTTPRequestHandler):
         # keeping them out of the lock lets the UI report 'initializing' while a
         # long equip (or a test script step) holds the card lock.  Result-shaping
         # masks everything card-derived when the session is not connected.
-        if self.path in ('/api/status', '/api/test/status'):
+        # Static PWA files are card-free too: they must stay answerable while a
+        # long card operation holds the lock (the server is threaded, so this
+        # bypass is what actually serves the modal's progress poll and page
+        # assets during a RAM install).
+        if self.path in ('/api/status', '/api/test/status') or not self.path.startswith('/api/'):
             self._do_GET()
             return
         # Serialize all card access: the background STATUS poll runs in its own