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>

go.mod

@@ -0,0 +1,18 @@
+module git.librete.ch/public/librenotes
+
+go 1.20
+
+require (
+	github.com/charlievieth/fastwalk v1.0.9 // indirect
+	github.com/gdamore/encoding v1.0.1 // indirect
+	github.com/gdamore/tcell/v2 v2.8.1 // indirect
+	github.com/junegunn/fzf v0.58.0 // indirect
+	github.com/junegunn/go-shellwords v0.0.0-20240813092932-a62c48c52e97 // indirect
+	github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/mattn/go-runewidth v0.0.16 // indirect
+	github.com/rivo/uniseg v0.4.7 // indirect
+	golang.org/x/sys v0.29.0 // indirect
+	golang.org/x/term v0.28.0 // indirect
+	golang.org/x/text v0.21.0 // indirect
+)