feat(biochem): Фаза 2.1/2.2/2.4 — серверный chem.js + /analyze + подсказки валентности

- biochem-core.js dual-export (browser window.BIO + Node module.exports), без дублей
- BIO.valency: подробные подсказки валентности (2.4), общие для редактора и сервера
- services/chem.js: серверный анализ поверх того же ядра (analyze/validate)
- POST /api/biochem/analyze (2.2); /validate переведён на ядро (+фикс формата связей)
- api.js: LS.biochemAnalyze

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

js/api.js

@@ -937,6 +937,7 @@ async function biochemGetElements()      { return req('GET', '/biochem/elements'
 async function biochemGetMolecules(p={}) { return req('GET', `/biochem/molecules?${new URLSearchParams(p)}`); }
 async function biochemGetMolecule(id)    { return req('GET', `/biochem/molecules/${id}`); }
 async function biochemValidate(atoms,bonds){ return req('POST','/biochem/validate',{atoms,bonds}); }
+async function biochemAnalyze(atoms,bonds){ return req('POST','/biochem/analyze',{atoms,bonds}); }
 async function biochemGetReactions()     { return req('GET', '/biochem/reactions'); }
 async function biochemGetChallenges()    { return req('GET', '/biochem/challenges'); }
 async function biochemSolveChallenge(id,payload)    { return req('POST',`/biochem/challenges/${id}/solve`,payload); }
@@ -1065,7 +1066,7 @@ window.LS = {
   clearFeaturesCache,
   hideDisabledFeatures,
   showBoardIfAllowed,
-  biochemGetElements, biochemGetMolecules, biochemGetMolecule, biochemValidate,
+  biochemGetElements, biochemGetMolecules, biochemGetMolecule, biochemValidate, biochemAnalyze,
   biochemGetReactions, biochemGetChallenges, biochemSolveChallenge,
   biochemGetSaved, biochemSave, biochemDeleteSaved,
   biochemGetPathways, biochemGetPathwayProgress, biochemSavePathwayProgress,