watcher.py: extend lockfile filter to catch UTF-8-mangled ~$ prefixes

Three rows in ingest_failures were Office lockfile leftovers whose
filename starts with ~� (~ followed by the UTF-8 replacement
character) instead of ~$. Somewhere in the Nextcloud sync chain the $
byte was lost or replaced; the file now lives on disk as a real file
with this corrupted name. The watcher's ("~$", ".") prefix filter
didn't match, so each cycle tried to ingest these as pptx, hit
BadZipFile inside python-pptx (lockfiles aren't real Office documents),
and they ended up permanently in ingest_failures.

Three filter sites in watcher.py applied the lockfile prefix check:
  - ingest_file() at :127
  - get_changed_files() at :200
  - IngestHandler._should_ignore() at :290

All three now match ("~$", "~", ".") — broadened to catch any tilde
prefix, not just ~$. The cross-check against pgvector embeddings and
disk found zero legitimate tilde-prefixed files in the corpus, so the
broader filter has no false-positive risk in this corpus.

Cleanup: 3 ingest_failures rows resolved (filepath LIKE '%/~%').
Unresolved count drops 97 → 94.

If a fourth filter site is ever added, the right shape is consolidating
the lockfile prefix check to a shared function or constant. Three
parallel sites with three different tuple orderings is acceptable for
now but worth normalizing if the surface grows.

scripts/watcher.py

@@ -124,7 +124,7 @@ def resolve_ingest_failure(source: str):
 
 
 def ingest_file(filepath: Path, embedder) -> int:
-    if filepath.name.startswith(("~$", ".")):
+    if filepath.name.startswith(("~$", "~", ".")):
         return 0
     if filepath.suffix.lower() not in SUPPORTED:
         return 0
@@ -197,7 +197,7 @@ def get_changed_files(state: dict) -> list:
             continue
         if path.suffix.lower() not in SUPPORTED:
             continue
-        if path.name.startswith((".", "~$")):
+        if path.name.startswith((".", "~$", "~")):
             continue
         if "Admin/Backups" in str(path) or "Backups" in path.parts:
             continue
@@ -287,7 +287,7 @@ class IngestHandler(FileSystemEventHandler):
         self.last_event = 0
 
     def _should_ignore(self, path: Path) -> bool:
-        if path.name.startswith((".", "~$")):
+        if path.name.startswith((".", "~$", "~")):
             return True
         if "Admin/Backups" in str(path) or "Backups" in path.parts:
             return True