feat(changelog): show every BREAKING headline in the default changelog view

[soustruh]

What was wrong

By default, kbagent changelog showed one line for each version: the first sentence of the first note. A BREAKING note that was not the first note stayed hidden until --full.

What changed

• For each version, the default view shows the first sentence of every BREAKING note.
• When a version has fewer than two BREAKING notes, the view adds the first other notes until two notes show.
• The notes keep their changelog order.
• The last shown line of a version ends with (+N more) when the version has other notes. The --full hint shows as before.
• --full, --json and the What's new notice after an update do not change.
• CHANGELOG_SUMMARY_NOTES in constants.py sets the minimum number of notes (2).
• --help, CLAUDE.md, commands-reference.md, context.py, CONTRIBUTING.md and the changelog.py docstring describe the new default.

Tests

• tests/test_changelog_render.py covers four cases. A version with two BREAKING notes shows only those. A version with one BREAKING note also shows its first other note. A version without one shows its first two notes. A version with two short notes hides nothing.
• Each of five mutations of the new selection fails a test: no fill for a single BREAKING note, BREAKING notes before the other notes, a fill of two notes also next to BREAKING notes, a case-sensitive prefix match, and (+N more) on the first line.
• make check passes.

No version bump, no changelog entry. The 0.96.0 release PR #817 adds the changelog entry.

[keboola-pr-reviewer-bot]

Verdict: auto_approve (risk 2/5) · profile keboola-mcp-server

Presentational-only change to the local kbagent changelog view, well-tested, with all doc surfaces updated.