feat: aplicação inicial — gerenciador de notas web estilo Mousepad

- Backend Go: API REST, auth por token (Bearer + cookie HttpOnly), storage em disco
  com revisões content-addressed (estilo Git: hash, autor, data, diff, restauração)
- Editor txt/md/html com preview, tags #tag, categorias, painel de histórico
- Preferências: números de linha, marcador de coluna (padrão 80), quebra de linha,
  fonte/tamanho, 4 temas e colorização de sintaxe (overlay no textarea)
- Frontend vanilla embutido via go:embed; Dockerfile multi-stage + docker-compose

internal/api/revisions.go

@@ -0,0 +1,112 @@
+package api
+
+import (
+	"net/http"
+	"regexp"
+	"slices"
+
+	"github.com/lgcosta/notas-online/internal/diffx"
+	"github.com/lgcosta/notas-online/internal/store"
+)
+
+var hashRe = regexp.MustCompile(`^[0-9a-f]{64}$`)
+
+func (s *Server) handleListRevisions(w http.ResponseWriter, r *http.Request) {
+	revs, err := s.st.History(r.PathValue("id"))
+	if err != nil {
+		mapStoreError(w, err)
+		return
+	}
+	// Mais recente primeiro: ordem natural para um painel de histórico.
+	slices.Reverse(revs)
+	if revs == nil {
+		revs = []store.Revision{}
+	}
+	writeJSON(w, http.StatusOK, revs)
+}
+
+func (s *Server) handleGetRevision(w http.ResponseWriter, r *http.Request) {
+	hash := r.PathValue("hash")
+	if !hashRe.MatchString(hash) {
+		writeError(w, http.StatusNotFound, "revisão não encontrada")
+		return
+	}
+	rc, err := s.st.RevisionWithContent(r.PathValue("id"), hash)
+	if err != nil {
+		mapStoreError(w, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, rc)
+}
+
+type diffView struct {
+	From    string `json:"from"`
+	To      string `json:"to"`
+	Author  string `json:"author"`
+	When    string `json:"when"`
+	Message string `json:"message"`
+	Diff    string `json:"diff"`
+	Added   int    `json:"added"`
+	Removed int    `json:"removed"`
+}
+
+func (s *Server) handleRevisionDiff(w http.ResponseWriter, r *http.Request) {
+	hash := r.PathValue("hash")
+	if !hashRe.MatchString(hash) {
+		writeError(w, http.StatusNotFound, "revisão não encontrada")
+		return
+	}
+	before, after, rev, err := s.st.DiffBetween(r.PathValue("id"), hash)
+	if err != nil {
+		mapStoreError(w, err)
+		return
+	}
+	from := "criação"
+	if rev.Parent != "" {
+		from = short(rev.Parent)
+	}
+	patch := diffx.Unified(from, short(hash), before, after)
+	added, removed := diffx.Stats(patch)
+	writeJSON(w, http.StatusOK, diffView{
+		From: from, To: short(hash), Author: rev.Author,
+		When: rev.When.Format("2006-01-02 15:04:05 MST"), Message: rev.Message,
+		Diff: patch, Added: added, Removed: removed,
+	})
+}
+
+type restoreInput struct {
+	Author string `json:"author"`
+}
+
+func (s *Server) handleRestore(w http.ResponseWriter, r *http.Request) {
+	hash := r.PathValue("hash")
+	if !hashRe.MatchString(hash) {
+		writeError(w, http.StatusNotFound, "revisão não encontrada")
+		return
+	}
+	var in restoreInput
+	if r.ContentLength > 0 {
+		if err := decodeJSON(r, &in, 1<<16); err != nil {
+			writeError(w, http.StatusBadRequest, "corpo JSON inválido")
+			return
+		}
+	}
+	n, err := s.st.Restore(r.PathValue("id"), hash, in.Author)
+	if err != nil {
+		mapStoreError(w, err)
+		return
+	}
+	content, _, err := s.st.Content(n.ID)
+	if err != nil {
+		mapStoreError(w, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, noteView{n, content})
+}
+
+func short(hash string) string {
+	if len(hash) > 8 {
+		return hash[:8]
+	}
+	return hash
+}