tools: fade_quads could not run -- two pre-monorepo paths

`screen-transitions.md` cites `fade_quads.py` as the command behind its decoded
fade ramp, and the command had been dead since the monorepo migration: it read
regn_decode.py from /work/Syplheed-Reborn and defaulted its pak to
/work/sylph_extract, neither of which exists. Resolve the helper beside the
script and default the pak under $SYLPHEED_DISC, the way run-canary and
sylpheed-cli already do.

A cited command that no longer runs is a citation nobody can check.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014voBspJ6kFncNErZJuZcLw

tools/re-capture/fade_quads.py

@@ -4,8 +4,12 @@
 The screen-transition fade lives here -- see docs/re/screen-transitions.md.
 Usage: PAK=<pak> fade_quads.py [build...]   (default: GP_TITLE, builds 2 4 5 6)"""
 import struct, sys, glob, os, zlib
-sys.path.insert(0, "/work/Syplheed-Reborn/tools/re-capture")
-src = open("/work/Syplheed-Reborn/tools/re-capture/regn_decode.py").read()
+# The monorepo migration left this pointing at /work/Syplheed-Reborn, a path
+# that no longer exists -- so the command screen-transitions.md cites as its
+# evidence could not be re-run.  Resolve beside this file instead.
+_SD = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, _SD)
+src = open(os.path.join(_SD, "regn_decode.py")).read()
 exec(src.split("# ── POF0")[0])
 
 DECL_AT, DECL_ENTRY, KF = 0x20, 60, 40
@@ -34,7 +38,10 @@ def parse(bundle):
         groups[idx]=g; pos=end
     return names, groups
 
-pak = os.environ.get("PAK", "/work/sylph_extract/dat/GP_TITLE.pak")
+# ...and the default pak pointed at /work/sylph_extract, which the disc mount
+# replaced.  $SYLPHEED_DISC is what run-canary and sylpheed-cli both use.
+pak = os.environ.get("PAK") or os.path.join(
+    os.environ.get("SYLPHEED_DISC", "/disc"), "dat", "GP_TITLE.pak")
 E = pak_entries(pak)
 E = [b for h,b in E]
 # build index -> pak entry index, from `screen list`: 0..9 then 12, 15