Fork Notesium source and restructure into Go package layout

Initial fork of github.com/alonswartz/notesium into librenotes:
- Source moved to internal/notesium/ (package notesium)
- Thin entry point at cmd/librenotes/main.go
- Module renamed to git.librete.ch/public/librenotes
- main() exposed as notesium.Run()
- LICENSE preserved (MIT), NOTICE added with attribution
- Web assets and completion.bash co-located with embedding code
  to satisfy go:embed path constraints

Closes #3, #34, #35.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/notesium/sort.go

@@ -0,0 +1,49 @@
+package notesium
+
+import (
+	"sort"
+	"strings"
+)
+
+type SortByCtime []*Note
+type SortByMtime []*Note
+type SortByTitle []*Note
+
+func (n SortByCtime) Len() int           { return len(n) }
+func (n SortByCtime) Less(i, j int) bool { return n[i].Ctime.After(n[j].Ctime) }
+func (n SortByCtime) Swap(i, j int)      { n[i], n[j] = n[j], n[i] }
+
+func (n SortByMtime) Len() int           { return len(n) }
+func (n SortByMtime) Less(i, j int) bool { return n[i].Mtime.After(n[j].Mtime) }
+func (n SortByMtime) Swap(i, j int)      { n[i], n[j] = n[j], n[i] }
+
+func (n SortByTitle) Len() int           { return len(n) }
+func (n SortByTitle) Less(i, j int) bool { return n[i].Title < n[j].Title }
+func (n SortByTitle) Swap(i, j int)      { n[i], n[j] = n[j], n[i] }
+
+func getSortedNotes(sortBy string) []*Note {
+	notes := make([]*Note, 0, len(noteCache))
+
+	for _, note := range noteCache {
+		notes = append(notes, note)
+	}
+
+	switch sortBy {
+	case "ctime":
+		sort.Sort(SortByCtime(notes))
+	case "mtime":
+		sort.Sort(SortByMtime(notes))
+	case "alpha":
+		sort.Sort(SortByTitle(notes))
+	}
+
+	return notes
+}
+
+func sortLinesByField(lines []string, separator string, fieldIndex int) {
+	sort.Slice(lines, func(i, j int) bool {
+		subI := strings.SplitN(lines[i], separator, fieldIndex+1)[fieldIndex]
+		subJ := strings.SplitN(lines[j], separator, fieldIndex+1)[fieldIndex]
+		return subI < subJ
+	})
+}