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.go

@@ -0,0 +1,119 @@
+package notesium
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// 1:semver (2:major 3:minor 4:patch 5:prerelease 6:prereleaseV) 7:commits 8:hash 9:dirty
+var gitVersionRegex = regexp.MustCompile(`^v((0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-(alpha|beta|rc)(?:\.(0|[1-9]\d*))?)?)-(0|[1-9]\d*)-g([0-9a-fA-F]+)(-dirty)?$`)
+
+var latestReleaseURL = "https://api.github.com/repos/alonswartz/notesium/releases/latest"
+
+type releaseInfo struct {
+	Version     string `json:"-"`
+	TagName     string `json:"tag_name"`
+	HTMLURL     string `json:"html_url"`
+	PublishedAt string `json:"published_at"`
+}
+
+func getVersion(gitVersion string) string {
+	if matches := gitVersionRegex.FindStringSubmatch(gitVersion); matches != nil {
+		semver := matches[1]
+		commits := matches[7]
+		isDirty := matches[9] == "-dirty"
+
+		if isDirty {
+			return fmt.Sprintf("%s+%s-dirty", semver, commits)
+		}
+
+		if commits != "0" {
+			return fmt.Sprintf("%s+%s", semver, commits)
+		}
+
+		return semver
+	}
+	return "0.0.0-dev"
+}
+
+func getLatestReleaseInfo() (releaseInfo, error) {
+	var release releaseInfo
+
+	req, err := http.NewRequest("GET", latestReleaseURL, nil)
+	if err != nil {
+		return release, fmt.Errorf("error creating request: %s", err)
+	}
+
+	req.Header.Set("Accept", "application/vnd.github+json")
+	req.Header.Set("X-GitHub-Api-Version", "2022-11-28")
+
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		return release, fmt.Errorf("error making request: %s", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return release, fmt.Errorf("error status code: %d", resp.StatusCode)
+	}
+
+	if err := json.NewDecoder(resp.Body).Decode(&release); err != nil {
+		return release, fmt.Errorf("error decoding response: %s", err)
+	}
+
+	if release.TagName == "" || release.HTMLURL == "" || release.PublishedAt == "" {
+		return release, fmt.Errorf("missing required field in response")
+	}
+
+	release.Version = strings.TrimPrefix(release.TagName, "v")
+	return release, nil
+}
+
+func compareVersions(v1, v2 string) int {
+	// returns -1 if v1 < v2, 1 if v1 > v2, and 0 if they are equal.
+	// v1: +build is ignored. -prerelease will decrement patch
+	// v2: +build is ignored. -prerelease not supported (set to 0.0.0)
+	normalize := func(v string, handlePreRelease bool) []int {
+		v = strings.SplitN(v, "+", 2)[0]
+		parts := strings.SplitN(v, "-", 2)
+		isPreRelease := len(parts) > 1
+
+		if isPreRelease && !handlePreRelease {
+			return []int{0, 0, 0}
+		}
+
+		versionParts := strings.Split(parts[0], ".")
+		for len(versionParts) < 3 {
+			versionParts = append(versionParts, "0")
+		}
+
+		intParts := make([]int, 3)
+		for i, part := range versionParts {
+			intParts[i], _ = strconv.Atoi(part)
+		}
+
+		if isPreRelease && handlePreRelease {
+			intParts[2]--
+		}
+
+		return intParts
+	}
+
+	v1Parts := normalize(v1, true)
+	v2Parts := normalize(v2, false)
+
+	for i := 0; i < 3; i++ {
+		if v1Parts[i] < v2Parts[i] {
+			return -1
+		} else if v1Parts[i] > v2Parts[i] {
+			return 1
+		}
+	}
+
+	return 0
+}