chore: cite docs/BUGS.md and drop references to notes outside the repo

66 comments cited `bugs.md B<n>`, the ledger's old name; they now say
`docs/BUGS.md B<n>`, and every cited number has an entry. About 90 more
cited offline.md, devices.md, features.md, mount-architecture.md,
plan.md and improvements.md, planning notes that were never in the
repository. Those citations are removed; the comments keep their text.

crates/pdfs-fuse/src/sync/engine.rs

@@ -33,7 +33,7 @@ pub(crate) enum SyncMsg {
     /// Re-read the folder set and adjust the filesystem watches (after add/remove).
     Rewatch,
     /// The daemon is tearing down: finish the current pass and end the engine
-    /// thread, so the mount can join it (bugs.md B44).
+    /// thread, so the mount can join it (`docs/BUGS.md` B44).
     Stop,
 }