Refactor case listing and silent recording handling

The case listing on the "My Cases" page is now grouped by local date,
with labels for "Heute", "Gestern", or the ISO date. This improves
readability and organization.

Additionally, the handling of silent recordings has been refined.
Previously, the absence of usable recordings would result in an error.
Now, the analysis worker gracefully handles this by writing a stub
document and skipping the LLM call. This prevents unnecessary errors and
provides a clearer status for silent cases.

The `dictate.sh` script has been updated to simplify the case directory
lookup logic. Instead of iterating through `open` and `done`
subdirectories, it now directly checks for the case ID and ensures it's
not marked as deleted. This simplifies the script and improves
efficiency.

The `server/Cargo.toml` and `server/Cargo.lock` have been updated to
include the `num_threads` dependency and enable additional features for
the `time` crate, which are necessary for proper local time zone
handling.

scripts/dictate.sh

@@ -43,12 +43,11 @@ fi
 # Locate a case directory under open/ or done/.
 case_dir_for() {
     local case_id="$1"
-    for sub in open done; do
-        if [ -d "$DATA_PATH/$SLUG/$sub/$case_id" ]; then
-            echo "$DATA_PATH/$SLUG/$sub/$case_id"
-            return 0
-        fi
-    done
+    local d="$DATA_PATH/$SLUG/$case_id"
+    if [ -d "$d" ] && [ ! -f "$d/.deleted" ]; then
+        echo "$d"
+        return 0
+    fi
     return 1
 }