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/runtime.go

@@ -0,0 +1,82 @@
+package notesium
+
+import (
+	"fmt"
+	"runtime"
+)
+
+type WebInfo struct {
+	Webroot      string `json:"webroot"`
+	Writable     bool   `json:"writable"`
+	StopOnIdle   bool   `json:"stop-on-idle"`
+	VersionCheck bool   `json:"daily-version-check"`
+}
+
+type BuildInfo struct {
+	GitVersion       string `json:"gitversion"`
+	Buildtime        string `json:"buildtime"`
+	GoVersion        string `json:"goversion"`
+	LatestReleaseURL string `json:"latest-release-url"`
+}
+
+type MemoryInfo struct {
+	MemoryAlloc      string `json:"alloc"`
+	MemoryTotalAlloc string `json:"total-alloc"`
+	MemorySys        string `json:"sys"`
+	MemoryLookups    uint64 `json:"lookups"`
+	MemoryMallocs    uint64 `json:"mallocs"`
+	MemoryFrees      uint64 `json:"frees"`
+}
+
+type RuntimeResponse struct {
+	Home     string     `json:"home"`
+	Version  string     `json:"version"`
+	Platform string     `json:"platform"`
+	Web      WebInfo    `json:"web"`
+	Build    BuildInfo  `json:"build"`
+	Memory   MemoryInfo `json:"memory"`
+}
+
+func GetRuntimeInfo(dir string, webOpts webOptions) RuntimeResponse {
+	var memStats runtime.MemStats
+	runtime.ReadMemStats(&memStats)
+
+	return RuntimeResponse{
+		Home:     dir,
+		Version:  getVersion(gitversion),
+		Platform: fmt.Sprintf("%s/%s", runtime.GOOS, runtime.GOARCH),
+		Web: WebInfo{
+			Webroot:      webOpts.webroot,
+			Writable:     !webOpts.readOnly,
+			StopOnIdle:   webOpts.heartbeat,
+			VersionCheck: webOpts.check,
+		},
+		Build: BuildInfo{
+			GitVersion:       gitversion,
+			Buildtime:        buildtime,
+			GoVersion:        runtime.Version(),
+			LatestReleaseURL: latestReleaseURL,
+		},
+		Memory: MemoryInfo{
+			MemoryAlloc:      bytesToHumanReadable(memStats.Alloc),
+			MemoryTotalAlloc: bytesToHumanReadable(memStats.TotalAlloc),
+			MemorySys:        bytesToHumanReadable(memStats.Sys),
+			MemoryLookups:    memStats.Lookups,
+			MemoryMallocs:    memStats.Mallocs,
+			MemoryFrees:      memStats.Frees,
+		},
+	}
+}
+
+func bytesToHumanReadable(bytes uint64) string {
+	const unit = 1024
+	if bytes < unit {
+		return fmt.Sprintf("%d B", bytes)
+	}
+	div, exp := int64(unit), 0
+	for n := bytes / unit; n >= unit; n /= unit {
+		div *= unit
+		exp++
+	}
+	return fmt.Sprintf("%.1f %cB", float64(bytes)/float64(div), "KMGTPE"[exp])
+}