v0.5.5

Documentation and packaging only. No code change, no behaviour change — still 23 tools and
2 prompts, and nothing about how the server runs is different from 0.5.4.

Added

• This changelog, covering all releases back to 0.1.0. Entries for 0.5.2 and earlier were
  backfilled from each release's own contemporaneous notes.
• A Changelog link on the PyPI project page, via a Changelog project URL.

Changed

• Release notes now come from this file. The release workflow extracts the tag's section and
  passes it to gh release create --notes-file, so GitHub, PyPI and the repo cannot drift
  apart. A missing section logs a warning and falls back to generated notes, so a release can
  never fail for want of prose.

  This replaces --generate-notes, which emitted PR-title lists. That was how 0.5.3 shipped a
  breaking change to tool output described only as "Fence tool output as untrusted database
  data" — accurate about the work, silent about the consequence.

• The notes for 0.5.2, 0.5.3 and 0.5.4 have been rewritten from their changelog entries.
  0.1.0 through 0.5.1 keep their original hand-written notes, which were already better than
  anything a regeneration would produce.

• Rule 7 (living documentation) now covers CHANGELOG.md, so entries are written with the
  change rather than remembered afterwards.