Check whether a brief echoes its loudest source

Product leadership plans each cycle from sales asks, support pain and strategy, and the loudest deal usually wins. An agent writes the planning brief, and a check measures whether each source's share of the brief matches its share of the evidence.

Write audit_brief_source_balance(channels, evidence_counts, brief_lines): the check every brief passes through.

• channels (list of str): the source channels, such as "sales".
• evidence_counts (list of int): how many pieces of evidence each channel contributed.
• brief_lines (list of int): how many lines of the brief each channel got.
• Index i in each list is one channel. Return one verdict per channel, in order, written "<channel>=over", "<channel>=under" or "<channel>=balanced".

Rules:

1. A channel's evidence share is its evidence count divided by the total evidence. Its brief share is its lines divided by the total lines. When a total is 0, every share of it is 0.
2. The skew is the brief share minus the evidence share.
3. A skew above 0.10: "over". Below -0.10: "under". Otherwise: "balanced".
4. Each channel is judged on its own numbers, even when two channels have the same name.