Preserve the policy footer and honor maxChars under constrained budgets

Greptile's runtime check found two pre-existing clamp gaps that matter
more now that the full policy emits once per session: the last-resort
tail slice cut the footer off an over-budget emission, and the DESIGN.md
staleness note was appended after clamping, pushing past maxChars.

The clamp now gives the footer the budget first, clipping the finding
line and downgrading full to short policy when needed. The staleness
note defers, without consuming its session flag, to a later emission
with room.

AI-assisted (Cursor agent), directed and reviewed by @abdulwahabone.

Co-authored-by: Cursor <cursoragent@cursor.com>

skill/scripts/hook-before-edit.mjs

@@ -476,7 +476,7 @@ async function main() {
   const footerMode = footerModeForSession(cache, sessionId);
   const message = appendDesignSystemNoteOnce(
     cursorBlockMessage(filtered, filePath, config, cwd, footerMode),
-    scanOptions, cache, sessionId,
+    scanOptions, cache, sessionId, config,
   );
   const denial = bumpCursorDenial(cache, sessionId, filePath, filtered);
   persistCache(cwd, cache);