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/version_test.go

@@ -0,0 +1,75 @@
+package notesium
+
+import (
+	"testing"
+)
+
+func TestGetVersion(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"v0.1.2-0-g1234567", "0.1.2"},
+		{"v0.1.2-2-g1234567", "0.1.2+2"},
+		{"v0.1.2-0-g1234567-dirty", "0.1.2+0-dirty"},
+		{"v0.1.2-2-g1234567-dirty", "0.1.2+2-dirty"},
+		{"v0.2.0-beta-0-g1234567", "0.2.0-beta"},
+		{"v0.2.0-beta-0-g1234567-dirty", "0.2.0-beta+0-dirty"},
+		{"v0.2.0-beta-2-g1234567", "0.2.0-beta+2"},
+		{"v0.2.0-rc.2-0-g1234567", "0.2.0-rc.2"},
+		{"v0.2.0-rc.2-0-g1234567-dirty", "0.2.0-rc.2+0-dirty"},
+		{"v0.2.0-rc.2-2-g1234567", "0.2.0-rc.2+2"},
+		{"v0.1.2-0-g1234567-foo", "0.0.0-dev"},
+		{"v0.1.2-foo-g1234567", "0.0.0-dev"},
+		{"0.1.2-0-g1234567", "0.0.0-dev"},
+		{"unset", "0.0.0-dev"},
+		{"foo", "0.0.0-dev"},
+		{"", "0.0.0-dev"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			result := getVersion(tt.input)
+			if result != tt.expected {
+				t.Errorf("getVersion(%s), want %s", result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestCompareVersions(t *testing.T) {
+	// -1 if v1 < v2, 1 if v1 > v2, and 0 if they are equal.
+	tests := []struct {
+		v1       string
+		v2       string
+		expected int
+	}{
+		{"", "", 0},
+		{"1.2.3", "", 1},
+		{"0.0.0", "", 0},
+		{"0.0.0-dev", "", -1},
+		{"0.0.0-dev", "1.2.3", -1},
+		{"1.2.3", "1.2.2", 1},
+		{"1.2.3", "1.2.3", 0},
+		{"1.2.3", "1.2.4", -1},
+		{"1.2.3+2", "1.2.2", 1},
+		{"1.2.3+2", "1.2.3", 0},
+		{"1.2.3+2", "1.2.4", -1},
+		{"1.2.3-beta", "1.2.1", 1},
+		{"1.2.3-beta", "1.2.2", 0},
+		{"1.2.3-beta", "1.2.3", -1},
+		{"1.2.3-beta", "1.2.4", -1},
+		{"1.2.0-beta", "1.2.0", -1},
+		{"1.2.0-beta", "1.2.4-beta", 1},
+		{"1.2.1-beta.2", "1.2.1", -1},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.v1+"_"+tt.v2, func(t *testing.T) {
+			result := compareVersions(tt.v1, tt.v2)
+			if result != tt.expected {
+				t.Errorf("compareVersions(%s, %s) = %d; want %d", tt.v1, tt.v2, result, tt.expected)
+			}
+		})
+	}
+}