#783 Audit inconsistent/missing copyright headers across .c/.h/CMakeLists.txt files

[Allen D Byrne]

Audit and standardize copyright/license header usage across the source tree. Current state is
inconsistent, quantified via a quick survey of app/bin, app/wlib, app/cornu, app/dynstring
(2026-09-07):

• .c files: 196 of 228 (86%) carry a Copyright line in their header comment; 32 have none at all.
• .h files: only 58 of 92 (63%) carry one -- headers are missing copyright notices noticeably more
  often than their matching .c files.
• CMakeLists.txt: 0 of 41 files anywhere in the repo carry any copyright/license text.

Among files that DO have a copyright line, the text itself is inconsistent -- different spacing/
punctuation ("Copyright (C) 2017" vs "Copyright (C)2017"), different author-joining conventions
("Dave Bullis and (C) 2007 Martin Fischer" vs "Dave Bullis, 2018 Martin Fischer" vs "Adam Richards
and Martin Fischer"), and no consistent policy on when a new contributor's name/year gets added to
an existing file's header vs. left alone.

Also worth a specific look: two files carry third-party (non-XTrkCAD-contributor) copyright lines
that appear to be genuine, deliberate vendored-code attribution rather than mistakes --
app/bin/stringxtc.c (Linus Torvalds) and app/bin/levenshtein.c / app/bin/include/levenshtein.h
(Titus Wormer, the well-known standalone levenshtein.c implementation). A reviewer should confirm
these attributions are complete/correct and that the surrounding license terms are actually
compatible with XTrkCAD's own GPL licensing, not just assume they're fine because they've always
been there.

This is a review/decision ticket, not yet a coding ticket: someone needs to decide (a) what the
canonical copyright header should look like going forward, (b) whether missing headers (.h and
CMakeLists.txt especially) should be backfilled or left alone, and (c) whether the third-party
attributions above need any follow-up. Once that's decided, the actual header-application work can
be split into normal bugs-tracker tickets/branches per area (e.g. one pass for app/bin, one for
app/wlib, one for CMakeLists.txt files), same pattern other bulk QA sweeps in this project have
used.