Include imported Still Alive data with disclaimer

Commit src/still_alive/imported.h instead of ignoring it. The importer now
writes a source reference (SDSkyKlouD/still-alive-web) and a disclaimer
(Jonathan Coulton / Valve, personal non-commercial use, not affiliated) at
the top of the file; the README carries the same disclaimer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/import_still_alive.py

@@ -10,7 +10,7 @@ placeholder lyrics.h / art.h / credits.h when it exists.
     python tools/import_still_alive.py --html index.html --js stillalive.js
     python tools/import_still_alive.py --out somewhere/imported.h
 
-imported.h is listed in .gitignore, so the imported text stays on your machine.
+imported.h is committed with a disclaimer and source reference at its top.
 
 Source format: each <div class="container_lyrics" data-start=ms> is one screen
 (the console clears when it starts). Inside it, <span data-start data-dur
@@ -153,8 +153,17 @@ def main():
         sys.exit("error: no lyrics, art or credits found; has the source changed?")
     check(steps, arts)
 
-    out = ["// Generated by tools/import_still_alive.py from",
-           "// https://github.com/SDSkyKlouD/still-alive-web - do not edit.",
+    out = ["// Song text, timing, ASCII art and credits from Portal's ending sequence,",
+           "// imported from still-alive-web by SD SkyKlouD:",
+           "//   https://github.com/SDSkyKlouD/still-alive-web",
+           "//",
+           "// Disclaimer: \"Still Alive\" was written by Jonathan Coulton for Portal (2007).",
+           "// Portal, its credits and ASCII art are (c) Valve Corporation, see",
+           "// https://store.steampowered.com/legal/. Included only for personal,",
+           "// non-commercial use in this hobby project; all rights remain with their",
+           "// owners. This project is not affiliated with or endorsed by Valve.",
+           "//",
+           "// Generated by tools/import_still_alive.py - do not edit by hand.",
            "#pragma once", "", '#include "show_data.h"', ""]
     for name, lines in arts.items():
         out.append(f"static const char* const ART_{name.upper()}_LINES[] = {{")