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/highlight.go

@@ -0,0 +1,175 @@
+package notesium
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strings"
+)
+
+const (
+	ansiHeading    = "\033[1m"
+	ansiBold       = "\033[1m"
+	ansiItalic     = "\033[3m"
+	ansiLink       = "\033[34m"
+	ansiCodeBlock  = "\033[33m"
+	ansiInlineCode = "\033[33m"
+	ansiBlockQuote = "\033[36m"
+	ansiListMarker = "\033[36m"
+	ansiReset      = "\033[0m"
+)
+var ansiLineBg = func() string {
+	switch os.Getenv("NOTESIUM_FINDER_THEME") {
+	case "light":
+		return "\033[48;5;7m"
+	default:
+		return "\033[40m"
+	}
+}()
+var (
+	reBold           = regexp.MustCompile(`\*\*(.*?)\*\*`)
+	reBoldAlt        = regexp.MustCompile(`__(.*?)__`)
+	reItalic         = regexp.MustCompile(`\*(.*?)\*`)
+	reItalicAlt      = regexp.MustCompile(`_(.*?)_`)
+	reUnorderedList  = regexp.MustCompile(`^(\s*[-+*]) `)
+	reOrderedList    = regexp.MustCompile(`^(\s*\d+\.) `)
+	reInlineCode     = regexp.MustCompile("`(.*?)`")
+	reLinkPlain      = regexp.MustCompile(`(?:https?://|www\.)[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}(/[^\s]*)?`)
+	reLinkMarkdown   = regexp.MustCompile(`\[(.[^]]*?)\]\((.[^)]*?)\)`)
+	reAnsi           = regexp.MustCompile(`\x1b\[[0-9;]*m`)
+	reReset          = regexp.MustCompile(`\x1b\[0m`)
+)
+
+func renderMarkdown(reader io.Reader, writer io.Writer, lineNumber int) {
+	inCodeBlock := false
+	scanner := bufio.NewScanner(reader)
+
+	for lineIndex := 1; scanner.Scan(); lineIndex++ {
+		line := scanner.Text()
+		highlightedLine := highlightLine(line, &inCodeBlock)
+		if lineNumber > 0 && lineNumber == lineIndex {
+			highlightedLine = highlightLineWithBackground(highlightedLine)
+		}
+		fmt.Fprintln(writer, highlightedLine)
+	}
+
+	if err := scanner.Err(); err != nil {
+		fmt.Fprintf(writer, "Error reading content: %v\n", err)
+	}
+}
+
+func highlightLine(line string, inCodeBlock *bool) string {
+	// Code blocks
+	if strings.HasPrefix(line, "```") {
+		*inCodeBlock = !*inCodeBlock
+		return ansiCodeBlock + line + ansiReset
+	}
+	if *inCodeBlock {
+		return ansiCodeBlock + line + ansiReset
+	}
+
+	// Headers
+	if strings.HasPrefix(line, "#") {
+		return ansiHeading + line + ansiReset
+	}
+
+	// Blockquotes
+	if strings.HasPrefix(line, "> ") {
+		return ansiBlockQuote + line + ansiReset
+	}
+
+	// Inline code
+	matches := reInlineCode.FindAllStringSubmatchIndex(line, -1)
+	if len(matches) > 0 {
+		return highlightLineWithInlineCode(line, matches)
+	}
+
+	return highlightString(line)
+}
+
+func highlightString(line string) string {
+	// Links
+	line = highlightLink(line, reLinkMarkdown, ansiLink)
+	line = highlightRegex(line, reLinkPlain, ansiLink, 0)
+
+	// Bold (**text** or __text__)
+	line = highlightRegex(line, reBold, ansiBold, 2)
+	line = highlightRegex(line, reBoldAlt, ansiBold, 2)
+
+	// Italic (*text* or _text_)
+	line = highlightRegex(line, reItalic, ansiItalic, 1)
+	line = highlightRegex(line, reItalicAlt, ansiItalic, 1)
+
+	// List markers
+	line = highlightRegex(line, reUnorderedList, ansiListMarker, 0)
+	line = highlightRegex(line, reOrderedList, ansiListMarker, 0)
+
+	return line
+}
+
+func highlightRegex(line string, re *regexp.Regexp, ansiCode string, markerLength int) string {
+	return re.ReplaceAllStringFunc(line, func(match string) string {
+		inner := match[markerLength : len(match)-markerLength]
+		return ansiCode + inner + ansiReset
+	})
+}
+
+func highlightLink(line string, re *regexp.Regexp, ansiCode string) string {
+	return re.ReplaceAllStringFunc(line, func(match string) string {
+		matches := re.FindStringSubmatch(match)
+		if len(matches) >= 2 {
+			title := matches[1]
+			return ansiCode + title + ansiReset
+		}
+		return match
+	})
+}
+
+func highlightLineWithInlineCode(line string, matches [][]int) string {
+	var builder strings.Builder
+	prevIndex := 0
+
+	for _, match := range matches {
+		start, end := match[0], match[1]
+		groupStart, groupEnd := match[2], match[3]
+
+		// Handle text before inline code
+		if start > prevIndex {
+			builder.WriteString(highlightString(line[prevIndex:start]))
+		}
+
+		builder.WriteString(ansiInlineCode)
+		builder.WriteString(line[groupStart:groupEnd])
+		builder.WriteString(ansiReset)
+
+		prevIndex = end
+	}
+
+	// Handle text after inline code
+	if prevIndex < len(line) {
+		builder.WriteString(highlightString(line[prevIndex:]))
+	}
+
+	return builder.String()
+}
+
+
+func highlightLineWithBackground(highlightedLine string) string {
+	// apply bg after resets to handle segments
+	highlightedLine = reReset.ReplaceAllStringFunc(highlightedLine, func(reset string) string {
+		return reset + ansiLineBg
+	})
+
+	// apply padding
+	termWidth := 79
+	visibleChars := len(reAnsi.ReplaceAllString(highlightedLine, ""))
+	requiredPadding := termWidth - visibleChars
+	if requiredPadding > 0 {
+		padding := strings.Repeat(" ", requiredPadding)
+		highlightedLine += ansiLineBg + padding
+	}
+
+	return ansiLineBg + highlightedLine + ansiReset
+}