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/filter.go

@@ -0,0 +1,83 @@
+package notesium
+
+import (
+	"strings"
+)
+
+func tokenizeFilterQuery(query string) []string {
+	tokens := []string{}
+	var currentToken string
+	var inQuotes bool
+	var quoteChar rune
+
+	for i := 0; i < len(query); i++ {
+		c := rune(query[i])
+
+		// If we're not in quotes and encounter a quote, we enter 'quote mode'
+		if !inQuotes && (c == '"' || c == '\'') {
+			inQuotes = true
+			quoteChar = c
+			continue
+		}
+
+		// If we are in quotes and encounter the same quoteChar, we exit 'quote mode'
+		if inQuotes && c == quoteChar {
+			inQuotes = false
+			continue
+		}
+
+		// If we're not in quotes and see a space, that's a token boundary
+		if !inQuotes && c == ' ' {
+			if currentToken != "" {
+				tokens = append(tokens, currentToken)
+				currentToken = ""
+			}
+			continue
+		}
+
+		// Otherwise, accumulate the character
+		currentToken += string(c)
+	}
+
+	// Append the last token if non-empty
+	if currentToken != "" {
+		tokens = append(tokens, currentToken)
+	}
+
+	return tokens
+}
+
+func evaluateFilterQuery(query string, input string) (bool, error) {
+	input = strings.ToLower(input)
+	tokens := tokenizeFilterQuery(strings.ToLower(query))
+	matches := true
+
+	for _, token := range tokens {
+		if strings.Contains(token, "|") {
+			// OR logic
+			terms := strings.Split(token, "|")
+			orMatch := false
+			for _, term := range terms {
+				if strings.Contains(input, term) {
+					orMatch = true
+					break
+				}
+			}
+			matches = matches && orMatch
+		} else if term, ok := strings.CutPrefix(token, "!"); ok {
+			// NOT logic
+			if strings.Contains(input, term) {
+				matches = false
+				break
+			}
+		} else {
+			// AND logic (implicit)
+			if !strings.Contains(input, token) {
+				matches = false
+				break
+			}
+		}
+	}
+
+	return matches, nil
+}