skills(ai): delete the planned-eval stub and drop its ceiling row

#14296 item 2 = A (comment 5507419465): the planned-eval stubs are
deleted and their ceilings step down; real fixtures stay, and no new
eval packages are created. This is round 2 of #14305 -- round 1 (PR
#14463, merged) implemented every RESTRUCTURE finding in
skills/objectstack-ai/SKILL.md and deferred AI-H-01 / AI-H-02, the
evals/README.md planned-structure stub, to this ruling.

Deletes skills/objectstack-ai/evals/README.md (315 tokens, 44 lines --
a placeholder whose "Structure" fence lists five eval files that do not
exist anywhere in the repo) and drops its one ceiling row from
scripts/check-skills-token-ratchet.mjs. That row was the only reference
to the path in the tree, so nothing else reads the file. No other row
changes, no ceiling raised.

skills/objectstack-ai/evals/ held nothing but the stub, so the ruling's
"real fixtures stay" clause has no subject here.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LraLgQVGq8egUwfYZpbYt1

Author: claude

scripts/check-skills-token-ratchet.mjs

@@ -437,7 +437,6 @@ export const CEILINGS = new Map([
   ['skills/objectstack-ui/evals/analytics-inline-vs-dataset.json', 1102],
 
   // the remaining skills' eval notes
-  ['skills/objectstack-ai/evals/README.md', 315],
 ]);
 
 /**