docs(changelog): order 0.16.0 bullets, linkify refs, fix historical section order (#22)

* docs(changelog): order 0.16.0 Added bullets feature-first, group transport typing

The 0.16.0 Added bullets landed in merge order rather than reading order:
MqttDeviceTransport (a derived type) led the list, ahead of the Device BYO
feature it serves and its own MqttTransport base, which trailed at the bottom.
Reorder to: Device BYO, will(), resync(), the MqttTransport/MqttControllerTransport
base typing, then MqttDeviceTransport right after it. Doc-only; 0.16.0 is already
released.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(changelog): linkify refs + @mentions; fix historical subsection order

GitHub only autolinks #N and @user inside issue/PR/commit/discussion bodies,
not in rendered repo files, so the CHANGELOG's bare refs were plain text.

- Linkify every #N and @cayossarian. #7 is the transport-seam *discussion*
  (/issues/7 404s), so it links to /discussions/7; every other #N links to
  /issues/N (GitHub redirects to /pull/N for PRs). @cayossarian -> profile.
- Canonical subsection order (Keep a Changelog): [0.14.0] had Fixed before
  Removed; [0.12.0] had Fixed before Added. Both corrected.

No entry content changed (74 bullets before and after); only order, links,
and one collapsed double-blank.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dcj