fix: correct conditional chain and add python -m tectonic fallback for both compile functions

app.py

@@ -394,8 +394,15 @@ def _compile_poster_pdf(OUTPUT_DIR: Path, logs):
             cmd = ["latexmk", "-pdf", "-interaction=nonstopmode", tex_path.name]
             logs.append("▶ Compiling with latexmk …")
         else:
-            logs.append("⚠️ No TeX engine found (tectonic/lualatex/xelatex/latexmk). Skipping PDF compile.")
-            return None
+            # try python -m tectonic if module is installed
+            try:
+                import importlib
+                importlib.import_module("tectonic")
+                cmd = [sys.executable, "-m", "tectonic", tex_path.name]
+                logs.append("▶ Compiling with python -m tectonic …")
+            except Exception:
+                logs.append("⚠️ No TeX engine found (tectonic/lualatex/xelatex/latexmk) and 'tectonic' module missing. Skipping PDF compile.")
+                return None
 
         proc = _sp.run(cmd, cwd=str(proj_dir), stdout=_sp.PIPE, stderr=_sp.STDOUT, text=True)
         if proc.stdout:
@@ -450,8 +457,14 @@ def _compile_tex_to_pdf(tex_path: Path, logs):
             cmd = ["latexmk", "-pdf", "-interaction=nonstopmode", tex_path.name]
             logs.append("▶ Compiling with latexmk …")
         else:
-            logs.append("⚠️ No TeX engine found.")
-            return None
+            try:
+                import importlib
+                importlib.import_module("tectonic")
+                cmd = [sys.executable, "-m", "tectonic", tex_path.name]
+                logs.append("▶ Compiling with python -m tectonic …")
+            except Exception:
+                logs.append("⚠️ No TeX engine found.")
+                return None
         proc = _sp.run(cmd, cwd=str(proj_dir), stdout=_sp.PIPE, stderr=_sp.STDOUT, text=True)
         if proc.stdout:
             logs.append(proc.stdout[-4000:])