refactor: remove dead code (#7911)

Remove verified-dead code surfaced by the #7911 simplification sweep
(all confirmed to have zero production references):

- util/create-sha-1-hash.ts (legacy local-file sync; had a broken
  import + leftover console.time)
- util/omit.ts, util/watch-object.ts, util/numeric-converter.ts
- selectAllTasksDueAndOverdue, selectTasksWorkedOnOrDoneFlat selectors
  (plus their specs and now-unused imports)
- getTagOrUndefined helper
- stale commented-out blocks in the task components
- dangling watch-object.ts reference in remove-unused-log-imports.ts

unschedule() was intentionally kept (still called internally), despite
being listed as dead.

scripts/remove-unused-log-imports.ts

@@ -21,7 +21,6 @@ const filesToFix = [
   'src/app/ui/duration/input-duration-formly/input-duration-formly.component.ts',
   'src/app/ui/inline-markdown/inline-markdown.component.ts',
   'src/app/util/is-touch-only.ts',
-  'src/app/util/watch-object.ts',
 ];
 
 function removeUnusedLogImport(filePath: string): void {