Add server-side folder picker

New GET /api/browse endpoint lists subdirectories at any path.
UI gets a folder icon button next to each path input that opens
a browsable directory tree modal. Escape or Cancel closes it,
clicking a folder navigates into it, Select confirms the choice.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/main.py

@@ -22,9 +22,22 @@ from pydantic import BaseModel
 import scanner as sc
 
 app = FastAPI(title="Duplicate Finder")
-templates = Jinja2Templates(directory="/app/templates")
 
-app.mount("/static", StaticFiles(directory="/app/static"), name="static")
+# Resolve paths relative to this file so it works both in Docker and locally
+_BASE = Path(__file__).parent
+_TEMPLATES_DIR = (
+    str(_BASE / "templates") if (_BASE / "templates").exists()
+    else str(_BASE.parent / "templates") if (_BASE.parent / "templates").exists()
+    else "/app/templates"
+)
+_STATIC_DIR = str(_BASE / "static")
+_STATIC_DIR = _STATIC_DIR if Path(_STATIC_DIR).exists() else "/app/static"
+# Ensure static dir exists
+Path(_STATIC_DIR).mkdir(parents=True, exist_ok=True)
+
+templates = Jinja2Templates(directory=_TEMPLATES_DIR)
+
+app.mount("/static", StaticFiles(directory=_STATIC_DIR), name="static")
 
 METHOD_META = {
     "sha256":   {"color": "#378ADD", "label": "Exact copy"},
@@ -502,6 +515,32 @@ def get_file_meta(file_id: int):
 
 # ── Stats ─────────────────────────────────────────────────────────────────────
 
+@app.get("/api/browse")
+def browse(path: str = Query("/")):
+    """List subdirectories at the given path for the folder picker."""
+    try:
+        p = Path(path).resolve()
+    except Exception:
+        raise HTTPException(400, "Invalid path")
+    if not p.exists() or not p.is_dir():
+        raise HTTPException(404, "Path not found")
+
+    dirs = []
+    try:
+        for entry in sorted(p.iterdir()):
+            if entry.is_dir() and not entry.name.startswith("."):
+                dirs.append(entry.name)
+    except PermissionError:
+        pass
+
+    parent = str(p.parent) if p != p.parent else None
+    return {
+        "current": str(p),
+        "parent": parent,
+        "dirs": dirs,
+    }
+
+
 @app.get("/api/stats")
 def get_stats():
     con = get_db()

app/scanner.py

@@ -35,7 +35,9 @@ VIDEO_EXT = {
 
 SUPPORTED_EXT = PHOTO_EXT | VIDEO_EXT
 
-DB_PATH = "/data/dupfinder.db"
+_DATA_DIR = Path("/data") if Path("/data").exists() else Path(__file__).parent.parent / "data"
+_DATA_DIR.mkdir(parents=True, exist_ok=True)
+DB_PATH = str(_DATA_DIR / "dupfinder.db")
 
 # Shared scan state (updated by background thread, read by status endpoint)
 scan_state = {