fix: security, correctness, and test hardening from review

- routes.py: reject glob wildcards (* ? [ ]) in skill name param to
  prevent rglob wildcard injection when serving linked files
- panels.js: replace inline onclick+esc() with data-* attributes and
  addEventListener for skill tag removal and linked-file clicks;
  esc() is HTML-safe but not JS-safe -- apostrophes in names caused
  JS syntax errors and _cronSelectedSkills array corruption
- ui.js: fix _fmtTokens(null/undefined) returning 'null'/'undefined'
  by guarding with (!n||n<0) -> '0'; add data-role attribute to msg-row
  elements so usage badge correctly targets the last assistant row
  instead of the last row regardless of speaker
- tests: rename test_sprint24.py -> test_sprint23.py (wrong sprint #);
  add 3 new tests: path traversal rejection, wildcard name rejection,
  cron create with skills; strengthen existing tests to assert field
  presence explicitly (was using .get(field, 0)==0 which never caught
  a missing field)

static/ui.js

@@ -82,7 +82,7 @@ let _scrollPinned=true;
     _scrollPinned=nearBottom;
   });
 })();
-function _fmtTokens(n){if(n>=1e6)return(n/1e6).toFixed(1)+'M';if(n>=1e3)return(n/1e3).toFixed(1)+'k';return String(n);}
+function _fmtTokens(n){if(!n||n<0)return'0';if(n>=1e6)return(n/1e6).toFixed(1)+'M';if(n>=1e3)return(n/1e3).toFixed(1)+'k';return String(n);}
 
 function scrollIfPinned(){
   if(!_scrollPinned) return;
@@ -426,7 +426,7 @@ function renderMessages(){
       inner.appendChild(thinkRow);
     }
     const row=document.createElement('div');row.className='msg-row';
-    row.dataset.msgIdx=rawIdx;
+    row.dataset.msgIdx=rawIdx;row.dataset.role=m.role||'assistant';
     let filesHtml='';
     if(m.attachments&&m.attachments.length)
       filesHtml=`<div class="msg-files">${m.attachments.map(f=>`<div class="msg-file-badge">&#128206; ${esc(f)}</div>`).join('')}</div>`;
@@ -488,9 +488,11 @@ function renderMessages(){
       else inner.appendChild(frag);
     }
   }
-  // Render per-turn usage badge on the last assistant message (if usage data exists)
+  // Render usage badge on the last assistant message row (if usage data exists)
   if(S.session&&(S.session.input_tokens||S.session.output_tokens)){
-    const lastAssist=inner.querySelector('.msg-row:last-child');
+    const rows=inner.querySelectorAll('.msg-row');
+    let lastAssist=null;
+    for(let i=rows.length-1;i>=0;i--){if(rows[i].dataset.role==='assistant'){lastAssist=rows[i];break;}}
     if(lastAssist&&!lastAssist.querySelector('.msg-usage')){
       const usage=document.createElement('div');
       usage.className='msg-usage';