kanban: README cites board_model.cpp:849 and :858 for the WIP-limit refusal; those lines are a tag guard and a closing brace

[Yaraslaut]

Found while fixing morph#368 and reported to the sprint manager rather than
absorbed, because it is pre-existing rather than introduced.

What is wrong

examples/kanban/README.md:112 cites two line numbers in board_model.cpp for
the WIP-limit refusal, and neither line contains it. On master e675253a:

the project (src/models/board_model.cpp:849, :858), Conflict for a …

Cited	What is actually there
:849	if (existingTags.empty()) {
:858	}

A tag-set guard and a closing brace. Nothing about a WIP limit, and nothing a
reader following the citation could act on.

Why it is worth a ticket

This is the same defect class as morph#349, morph#355 and morph#419 — a comment
or document citing a location that has since moved — but in a rung README,
which is the document a newcomer reads to learn how the ladder demonstrates the
framework. examples/IMPLEMENTATION.md treats a rung's README as part of what
the rung ships, and scripts/check_spec_citations.sh verifies cited paths and
section headings but not line numbers, so nothing catches this and nothing
will.

It was already wrong before morph#368's branch existed — confirmed by reading
origin/master directly, not the working tree — so it is neither introduced by
that work nor fixed by it.

Verification status: reproduced

$ git show origin/master:examples/kanban/README.md | grep -nE "board_model\.cpp:[0-9]+"
112:   the project (`src/models/board_model.cpp:849`, `:858`), `Conflict` for a
$ git show origin/master:examples/kanban/src/models/board_model.cpp | sed -n '849p;858p'
    if (existingTags.empty()) {
    }

Not verified: whether other rung READMEs carry the same rot. Only kanban's
was checked, because that is the rung morph#368 was in. A sweep across
examples/*/README.md is the obvious next question and may widen this ticket.

What would close this

1. examples/kanban/README.md:112 cites the line that actually raises the
   WIP-limit refusal, verified by reading it rather than by assuming a fixed
   offset.
2. Every other board_model.cpp:NNN citation in that README is checked the same
   way, not just the two named here.
3. A statement either way on whether the other rung READMEs were swept — if they
   were not, say so, so the next reader knows the scope of what was fixed.

Not closable by deleting the citations. They are pointing at something real;
the location moved.