repo: remove superseded pilot files, ASCII-clean the build and nginx configs

Drops the legacy course-1 template, the two python assemblers the node
assembler replaced, and the unversioned scene manifest left over from the
manifest-<type> split - none referenced by build.sh, the assembler or the
README, and none produce build output. The v2 pages stay: the README lists
them as parked. Also converts typographic dashes to ASCII in build.sh and the
two nginx configs, and corrects an assembler comment that still pointed at the
removed python build.

nginx/security-headers.conf

@@ -1,5 +1,5 @@
 # Shared security headers. `include`d in the server block AND in every location that
-# sets its own add_header — a location-level add_header REPLACES inherited headers
+# sets its own add_header - a location-level add_header REPLACES inherited headers
 # rather than merging them (the classic nginx footgun).
 #
 # HSTS is host-scoped: NO includeSubDomains / preload, because the *.bztmon.com