docs: point format spec to the external feedpak-spec repo

The 940-line format developer guide has moved to its own published repo,
got-feedback/feedback-feedpak-spec (released as feedpak v1.0.0). Replace
docs/sloppak-spec.md with a thin pointer at the same path so existing
references keep resolving; it links to the authoritative spec, bridges the
sloppak/feedpak naming, and keeps the feedback-specific "where it lives in
lib/" implementation map.

Also repoint the human-facing references — CLAUDE.md's developer-reference
link, the constitution's format reference, and the hand-editing guide's
cross-links (to the spec's renumbered §6/§8/§9.5). The hand-editing guide
itself stays: its practical "edit your own pack" content is not in the spec
repo. Inline code comments that cite old "sloppak-spec §X.Y" section numbers
are left for a follow-up (the path still resolves; numbers are approximate).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Kris Anderson <topkoa@gmail.com>

.specify/memory/constitution.md

@@ -100,7 +100,9 @@ do not collide in `sys.modules`.
 The whole point of Slopsmith is that a user points it at an existing
 song library folder and it Just Works. The library is scanned and
 indexed in `meta.db` (SQLite via `MetadataDB`). The open Sloppak
-format (`lib/sloppak.py`, `docs/sloppak-spec.md`) is the preferred
+format (`lib/sloppak.py`; specified at
+[got-feedback/feedback-feedpak-spec](https://github.com/got-feedback/feedback-feedpak-spec),
+published as feedpak — same format) is the preferred
 format and the home for new features; loose-folder XML charts
 (`lib/loosefolder.py`) are also discovered and played as a first-class
 format. Both must keep playing across releases.