fix(naming): merge duplicate [section] blocks in the language table

F1 (review round 1): of_string's find took only the FIRST section of a
given name (List.find_opt), so a second [celebration] block anywhere in
the file was silently dropped in its entirety -- reproduced with two
blocks (a in the first, b in the second): b resolved to the slug
fallback "b", not its real value.

This is a data-loss footgun aimed squarely at what happens next: Tasks
3/4 write a 595-entry, hand-edited la.ini, and appending a second
[celebration] block is the natural way to paste in a new batch of names.
Worse, the failure surfaces nowhere near its cause -- a coverage check
reports the dropped slugs as missing a Latin name, with nothing pointing
at the parser.

find now folds over every section sharing the name, in file order, so
all blocks merge. This also settles which value wins when the same key
appears in two different blocks: later in the file wins, consistent with
the existing within-one-block behaviour (unchanged, still last SM.add
wins) and with what a reader expects when appending to an INI file.

lang.mli now documents both duplicate policies explicitly, and notes
they run OPPOSITE to Overlay_ini.get's first-match (List.assoc_opt) over
the same section.fields shape -- undocumented before, and a latent trap
since the two modules read the same section type but resolve a
duplicate key in opposite directions.

Three tests added: two [celebration] blocks both resolve (the F1
regression), a key repeated across two blocks resolves to the later
block, and a key repeated within one block still resolves to the later
line (confirms unchanged behaviour). Confirmed the regression test fails
against the pre-fix code (b resolves to "b", the slug fallback) and
passes after.

0 files changed, 0 insertions, 0 deletions