Please address the comments from this code review:

## Overall Comments
- The special-case `readonly`/`unable to open` branch currently assumes a directory permissions issue; consider broadening the message to mention both file and directory permissions (or phrasing it more generically) since these errors can also arise from file-level ACLs or missing paths.
- When constructing `db_dir = os.path.dirname(dbpath)`, it may be safer to normalize the path (e.g., via `os.path.abspath`) and handle the case where `dbpath` has no directory component, so that the resulting message about the directory being writable is always meaningful.

## Individual Comments

### Comment 1
<location> `beets/ui/__init__.py:1513-1518` </location>
<code_context>
+        # Check for permission-related errors and provide a helpful message
+        error_str = str(db_error).lower()
+        dbpath_display = util.displayable_path(dbpath)
+        if "readonly" in error_str or "unable to open" in error_str:
+            db_dir = os.path.dirname(dbpath)
+            raise UserError(
+                f"database file {dbpath_display} could not be opened due to a "
+                f"permissions error. Please check that the directory "
+                f"{util.displayable_path(db_dir)} is writable."
+            )
         raise UserError(
</code_context>

<issue_to_address>
**issue (bug_risk):** The permission-specific branch may misdiagnose non-permission errors as permission issues.

Relying on the generic substring `"unable to open"` and mapping it directly to a permissions error is brittle. This message can also arise from non-permission issues (missing directory, malformed path, unavailable filesystem). Please either narrow the pattern to permission-specific cases, include the original `db_error` in the message for context, or soften the wording so it doesn’t claim permissions are the only cause.
</issue_to_address>

### Comment 2
<location> `beets/ui/__init__.py:1512-1522` </location>
<code_context>
+        dbpath_display = util.displayable_path(dbpath)
+        if "readonly" in error_str or "unable to open" in error_str:
+            db_dir = os.path.dirname(dbpath)
+            raise UserError(
+                f"database file {dbpath_display} could not be opened due to a "
+                f"permissions error. Please check that the directory "
+                f"{util.displayable_path(db_dir)} is writable."
+            )
         raise UserError(
</code_context>

<issue_to_address>
**suggestion:** The permission-focused message drops the original SQLite error details, reducing debuggability.

In this branch, the original `db_error` isn’t surfaced, unlike in the generic error path. Please include it here as well (e.g., by appending `f" (original error: {db_error})"`) so callers retain the underlying SQLite details for troubleshooting.

```suggestion
        dbpath_display = util.displayable_path(dbpath)
        if "readonly" in error_str or "unable to open" in error_str:
            db_dir = os.path.dirname(dbpath)
            raise UserError(
                f"database file {dbpath_display} could not be opened due to a "
                f"permissions error. Please check that the directory "
                f"{util.displayable_path(db_dir)} is writable "
                f"(original error: {db_error})."
            )
        raise UserError(
            f"database file {dbpath_display} could not be opened: {db_error}"
        )
```
</issue_to_address>