model: add missing build_cvec to plamo2

[nisparks]

Summary

PLaMo-2 is missing the build_cvec() call in its graph builder, causing --control-vector to be silently ignored.

Root Cause

PR #20653 ("model: add control vector support where missing") touched both plamo2.cpp and plamo3.cpp, but the plamo2 change was incomplete.

Comparing the diffs from #20653:

plamo3.cpp — correct (3 lines added):

        cur = build_cvec(cur, il);
        cb(cur, "l_out", il);

        // input for next layer

plamo2.cpp — incomplete (only the comment was added):

        // input for next layer

The actual build_cvec() and cb() calls were missed.

Fix

Adds the missing two lines, matching the pattern in plamo3.cpp and all other 100+ model implementations:

        cur = build_cvec(cur, il);
        cb(cur, "l_out", il);

Impact

• Without fix: --control-vector silently does nothing on PLaMo-2
• With fix: Control vectors are applied per-layer as intended
• Risk: Zero — build_cvec is a no-op when no control vector is loaded, so normal inference is completely unaffected

[ggml-gh-bot]

Hi @nisparks, thanks for your contribution!

Per our contribution guidelines, the automated PR checker found the following issue(s) that need your attention:

• Multiple open PRs from a new contributor: We limit new contributors (those without a previously merged PR) to 1 open PR at a time. You currently have 2 open PRs.

• AI-generated content: This project does not accept PRs, descriptions or commit messages that are fully or predominantly AI-generated. If you have used AI to assist you in writing code, please make sure to disclose that explicitly.

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Please note that maintainers reserve the right to make final decisions on PRs. If you believe there is a mistake, please comment below.

[CISC]

Not missed, but rather purposefully left out, see #20653 (review)

Also, please read and conform to our contribution guidelines in the future.