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/completion.bash

@@ -0,0 +1,49 @@
+__notesium_cmds() {
+    notesium help 2>&1 | awk '/^  [a-z\-]/ {print $1}'
+}
+
+__notesium_opts() {
+    notesium help 2>&1 | \
+        awk '/^  [a-z]/ {cmd=$1}; /^    --/ {print cmd, $1}' | \
+        awk -v cmd="^$1\ " '$0 ~ cmd {print $2}' | \
+        sed 's/--sort=WORD/--sort=ctime\n--sort=mtime\n--sort=alpha/' | \
+        sed 's/--prefix=WORD/--prefix=ctime\n--prefix=mtime\n--prefix=label/'
+}
+
+__notesium_complete() {
+    local words
+    case "${#COMP_WORDS[@]}" in
+        2) words="$(__notesium_cmds)";;
+        *) words="$(__notesium_opts ${COMP_WORDS[1]})";;
+    esac
+
+    # handle options with equals. COMP_WORDBREAKS is global.
+    _get_comp_words_by_ref -n = cur prev
+
+    if [[ "${COMP_WORDS[1]}" == "finder" ]]; then
+        if [[ "${prev}" == "--" ]]; then
+            words="$(echo -e "list\nlinks\nlines")"
+        else
+            for ((i = 1; i < ${#COMP_WORDS[@]} - 1; i++)); do
+                if [[ "${COMP_WORDS[i]}" == "--" ]]; then
+                    words="$(__notesium_opts "${COMP_WORDS[i+1]}")"
+                    break
+                fi
+            done
+        fi
+    fi
+
+    case ${cur} in
+        --prefix=*|--sort=*)
+            prev="${cur%%=*}="
+            cur="${cur#*=}"
+            words="$(echo "$words" | awk -F "=" -v p="^$prev" '$0 ~ p {print $2}')"
+            COMPREPLY=($(compgen -W "$words" -- "${cur}"))
+            return 0
+            ;;
+    esac
+
+    COMPREPLY=($(compgen -W "$words" -- "${COMP_WORDS[COMP_CWORD]}"))
+}
+
+complete -o default -F __notesium_complete notesium