Cleanup: dead code, small fixes, Library sorts, old-UI links (#620) (#621)

* refactor: remove dead and test-only code and the write-only prompt registry (#620)

Removes helpers nothing calls, test-only wrappers and their tests, the unused
config writer, three unused images, and the prompt registry the nodes wrote to
but nothing read, which grew with every run.

* fix: network-share readers, model unload off the loop, bad save requests (#620)

Every read-only SQLite open now uses one URI helper, so a library on a Windows
network share works in backups, restores, moves and history reads. Unloading a
model no longer blocks the server. A malformed /save body gets a 400, not a 500.

* feat(library): add Recently used, Most used and Name Z-A sorting (#620)

The old Dashboard's sorts the community asked for, on the Prompt library, in
saved views, and with paging through the whole list.

* feat(workspace): stop linking the old pages (#620)

They show a removal notice since 3.5.1. System no longer links them, the load
failure offers a reload and ComfyUI instead, and the README says they are going
away. The pages still work at their URLs.

web/js/workspace/workspace.css

@@ -575,7 +575,6 @@ pre.prompt-text { font: inherit; font-size: 12px; line-height: 1.75; margin-bloc
 }
 .more-menu-list[hidden] { display: none; }
 .more-menu-list > button { justify-content: flex-start; text-align: left; width: 100%; white-space: nowrap; }
-.legacy-pages { margin: 16px 0 0; color: var(--muted); /* D165 */ }
 
 /* D164 (#524): the prompt page has four heading actions and titles of any length, which the concept never shows. From
    the concept's sidebar breakpoint up the actions keep one row and the title takes what is left, clamped to two lines