feat(import): v5.6.0 unified data import (phases 0-5)

- unified importer framework (app/services/importers/): normalized model,
  registry, common pipeline (hierarchy, attachments, collections, dedup),
  async jobs, dry-run preview, column->type mapping
- Phase 1: Obsidian, Notion, Logseq/Roam, HTML (Apple Notes/Bear/Ulysses/
  OneNote), Google Keep, generic Markdown
- Phase 2: typed CSV/TSV, Excel (openpyxl), generic JSON
- Phase 3: Word .docx (python-docx), PDF (pypdf), HTML folders
- Phase 4: Raindrop, Pocket, Readwise, Shaarli, Netscape bookmarks, .ics,
  OPML, Standard Notes, Gitea/GitHub issues (+labels/milestones)
- Phase 5: incremental re-sync (skip/update/duplicate), partial-error resume,
  forge repo files, URL web clipper (SSRF guard), batch multi-file + UI queue,
  Notion relation resolution, exportable JSON reports
- /import wizard, API /api/import/*, migration 9 (import_items, import_jobs)
- fix: property values stored by property id (correct DB view rendering)
- deps: openpyxl, beautifulsoup4, PyYAML, python-docx, pypdf
- 43 import tests; full suite 491 green; ruff clean
- bump version 5.11.5

app/services/importers/markdown.py

@@ -0,0 +1,87 @@
+"""FlowDeck — generic Markdown / text importer (v5.6.0, Phase 1)."""
+from __future__ import annotations
+
+import io
+import zipfile
+
+from app.services.importers.base import (
+    Importer,
+    ImportPage,
+    ImportResult,
+    decode_text,
+    register_importer,
+)
+
+_MD_EXTS = (".md", ".markdown", ".txt", ".mdx")
+
+
+def _title_from_name(name: str) -> str:
+    base = name.replace("\\", "/").rsplit("/", 1)[-1]
+    for ext in (".markdown", ".markdown", ".mdx", ".md", ".txt"):
+        if base.lower().endswith(ext):
+            base = base[: -len(ext)]
+            break
+    return base.strip() or "Untitled"
+
+
+@register_importer
+class MarkdownImporter(Importer):
+    source_id = "markdown"
+    label = "Markdown / texte"
+    description = "Fichiers .md/.markdown/.txt ou archive .zip de fichiers Markdown."
+    extensions = (".md", ".markdown", ".txt", ".zip")
+    order = 90
+
+    def detect(self, filename: str, data: bytes) -> bool:
+        low = filename.lower()
+        if low.endswith(_MD_EXTS):
+            return True
+        if low.endswith(".zip"):
+            try:
+                zf = zipfile.ZipFile(io.BytesIO(data))
+            except (zipfile.BadZipFile, OSError):
+                return False
+            names = [n for n in zf.namelist() if not n.endswith("/")]
+            return bool(names) and all(n.lower().endswith(_MD_EXTS) for n in names)
+        return False
+
+    def parse(self, filename: str, data: bytes) -> ImportResult:
+        result = ImportResult(source=self.source_id)
+        if filename.lower().endswith(".zip"):
+            try:
+                zf = zipfile.ZipFile(io.BytesIO(data))
+            except (zipfile.BadZipFile, OSError) as exc:
+                result.warn(f"Archive invalide : {exc}")
+                return result.finalize()
+            entries = sorted(
+                (n for n in zf.namelist()
+                 if not n.endswith("/") and n.lower().endswith(_MD_EXTS)),
+                key=lambda n: (n.count("/"), n.lower()),
+            )
+            if not entries:
+                result.warn("Aucun fichier Markdown trouvé dans l'archive")
+                return result.finalize()
+            for name in entries:
+                try:
+                    text = decode_text(zf.read(name))
+                except Exception as exc:  # noqa: BLE001
+                    result.warn(f"Lecture impossible : {name} ({exc})")
+                    continue
+                parts = name.replace("\\", "/").split("/")
+                result.pages.append(ImportPage(
+                    title=_title_from_name(name),
+                    markdown=text,
+                    source_path=name,
+                    parent_path="/".join(parts[:-1]),
+                    external_id=name,
+                ))
+            return result.finalize()
+
+        text = decode_text(data)
+        result.pages.append(ImportPage(
+            title=_title_from_name(filename),
+            markdown=text,
+            source_path=filename,
+            external_id=filename,
+        ))
+        return result.finalize()