Wraps Outline's Comments API in OutlineKit for the first time -
comments.list is documented in the vendored spec; comments.resolve/
unresolve are not, confirmed real against Outline's own server source
instead of guessed. Comment bodies are ProseMirror documents (data),
not plain text - added a small recursive JSONValue tree plus a
best-effort plainText() walk for display, since nothing here needs to
write comment bodies back (out of scope for this pass, see
DocumentCommentsSheet's doc comment).
Reader toolbar gets a marker (bubble icon + count badge) only when
the document actually has comments, per explicit instruction that
this should be a simple symbol rather than a true in-document gutter
marker at each comment's anchor position - anchoring is plain-text-
substring-based server-side and doesn't map cleanly onto this app's
own Markdown rendering. Opens a read-only comment list with a
Resolve/Unresolve toggle per the confirmed scope for this pass; no
creating or replying yet.