… fileId

Two related bugs in the comments flow:

1. getOrCreateSpaceFile (files-queries.service.ts) could create duplicate
   rows in the `files` table. When a file was not yet indexed, repeated
   calls with a non-positive fileId always fell through to INSERT without
   first checking whether a record already existed at that path. Because
   the table has no unique constraint on the path columns, this silently
   accumulated duplicates. On the next directory browse, browseFiles and
   getSpaceFileId could disagree on which row to return (iteration order
   vs LIMIT 1), producing a spurious "File id mismatch" on subsequent
   comment operations.

   Fix: call getSpaceFileId before the fallthrough INSERT and return the
   existing id if one is found, so the insert only happens when no record
   exists at that path.

2. updateComment and deleteComment declared their local fileId as
   `number` even though getFileId can return undefined when the file is
   not indexed. TypeScript silently accepted the mistyped value, making
   the mismatch check always true for an unindexed file and throwing
   "File id mismatch" instead of an accurate error.

   Fix: remove the `: number` annotation so TypeScript infers
   `number | undefined`, and add an explicit `fileId === undefined`
   guard before the mismatch comparison — matching the pattern already
   present in createComment.

   Also fix createComment to handle getFileId returning undefined when
   the caller supplies a positive fileId: instead of throwing mismatch,
   delegate to getOrCreateSpaceFile to index the file on demand.

Tests: add three new cases to comments-manager.service.spec.ts covering
each of the fixed branches (createComment with unindexed positive id,
updateComment with undefined fileId, deleteComment with undefined fileId).