license: relicense clectio's own code under GPL-3.0-or-later

Replace the ISC licence with GPL-3.0-or-later (Łukasz Kasprzak is sole
copyright holder, so relicensing is unencumbered):

- LICENSE: verbatim GNU GPL v3 text.
- Add "Copyright (C) 2026 Łukasz Kasprzak. SPDX-License-Identifier:
  GPL-3.0-or-later" headers to the project-authored sources (clectio.c with the
  full grant, plus mktext.c and bin2h.c), replacing their old public-domain
  notes.
- puff.c/.h keep Mark Adler's public-domain notice unchanged: third-party,
  not ours to relicense, and public domain is GPL-compatible.
- README and man page LICENSE sections updated to GPL-3.0-or-later, noting
  puff's PD status; the scripture-text carve-out (Vulgate public domain,
  corpora under their own terms) is preserved.

Code/comment change only; builds clean under -Wall -Wextra.

Claude-Session: https://claude.ai/code/session_01S1CD1u3tgSS4xNu6WHfp5a

1 files changed, 2 insertions, 0 deletions

diff --git a/mktext.c b/mktext.c
index 17d7705..8f07f14 100644
--- a/mktext.c
+++ b/mktext.c
@@ -7,6 +7,8 @@
  *
  * usage: mktext verses.keys corpus.tsv out.lz
  *   out.lz = [uint32 LE rawlen][LZSS-packed "chap:verse text\n" lines].
+ *
+ * Copyright (C) 2026 Łukasz Kasprzak.  SPDX-License-Identifier: GPL-3.0-or-later
  */
 #include <stdio.h>
 #include <stdlib.h>