fix: collision names must survive the sanitiser the content view applies

unique_filename produced 'manual (2).pdf'; HouseplanContentView sanitises the
name in the REQUEST too, turning ' (2)' into '_2_', so the file was written and
then 404'd. The same pattern was already in files/migrate, so a rebind that hit
a name collision has been producing dead links. Both use the shared helper now,
with '-2', which round-trips sanitize_filename — asserted.

custom_components/houseplan/plans.py

@@ -35,7 +35,11 @@ def unique_filename(directory: Path, name: str) -> str:
         stem, suffix = safe, ""
     i = 2
     while True:
-        candidate = f"{stem} ({i}){'.' + suffix if suffix else ''}"
+        # "-2", not " (2)": the content view sanitizes the name in the REQUEST
+        # too, and a space or a bracket there turns into "_", so a file called
+        # "manual (2).pdf" was written and then never served. Only characters
+        # that survive sanitize_filename may be used to build a name.
+        candidate = f"{stem}-{i}{'.' + suffix if suffix else ''}"
         if not (directory / candidate).exists():
             return candidate
         i += 1

custom_components/houseplan/websocket_api.py

@@ -20,7 +20,7 @@ from .const import (
     CONTENT_URL, FILES_DIR, MAX_SIGN_PATHS, PLANS_DIR, PLANS_URL,
 )
 from .auth import may_write
-from .plans import collect_attachments, collect_plans
+from .plans import collect_attachments, collect_plans, unique_filename
 from .store import HouseplanData, get_data, get_entry
 from .validation import (
     CONFIG_SCHEMA, LAYOUT_SCHEMA, MAX_CONFIG_BYTES, MAX_PLAN_BYTES,
@@ -193,15 +193,10 @@ async def ws_files_migrate(hass: HomeAssistant, connection, msg: dict[str, Any])
         for f in sorted(src.iterdir()):
             if not f.is_file():
                 continue
-            target = dst / f.name
-            if target.exists():
-                # a different file already owns this name — do NOT silently
-                # point the url at it; give the copy a unique name instead
-                stem, suffix = f.stem, f.suffix
-                i = 2
-                while (dst / f"{stem} ({i}){suffix}").exists():
-                    i += 1
-                target = dst / f"{stem} ({i}){suffix}"
+            # a different file may already own this name — do NOT silently point
+            # the url at it; the shared helper picks a free one, using only
+            # characters the content view will accept back in a request
+            target = dst / unique_filename(dst, f.name)
             shutil.copy2(str(f), str(target))
             mapping[f.name] = target.name
         return mapping