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/finder.go

@@ -0,0 +1,54 @@
+package notesium
+
+import (
+	"fmt"
+
+	fzf "github.com/junegunn/fzf/src"
+)
+
+type channelWriter struct {
+	ch chan string
+}
+
+func (cw *channelWriter) Write(p []byte) (n int, err error) {
+	str := string(p) // Convert bytes to string
+	cw.ch <- str     // Send to channel
+	return len(p), nil
+}
+
+func runFinder(inputChan chan string, opts []string) ([]string, int, error) {
+	options, err := fzf.ParseOptions(false, opts)
+	if err != nil {
+		return nil, 2, fmt.Errorf("fzf error: %w", err)
+	}
+
+	outputChan := make(chan string)
+	resultChan := make(chan struct {
+		code int
+		err  error
+	}, 1)
+
+	options.Input = inputChan
+	options.Output = outputChan
+
+	go func() {
+		code, runErr := fzf.Run(options)
+		close(outputChan)
+
+		resultChan <- struct {
+			code int
+			err  error
+		}{code, runErr}
+
+		close(resultChan)
+	}()
+
+	var lines []string
+	for line := range outputChan {
+		lines = append(lines, line)
+	}
+
+	result := <-resultChan
+	return lines, result.code, result.err
+}
+