Upgrade to Sonnet 4.6 + add Gemini 3.1 Pro support

- Refactored analyze_with_claude into shared _build_analysis_prompt + _parse_llm_response helpers
- New analyze_with_gemini() using Gemini 3.1 Pro ($2/M in, MMMLU 92.6% — best multilingual)
- Unified analyze_with_llm(provider) dispatcher with auto-fallback (Claude → Gemini)
- API endpoint accepts llm_provider in StartJobIn (claude/gemini/auto)
- Frontend dropdown to pick LLM
- Default model is now Sonnet 4.6 (was Haiku 4.5) — 3x quality at 3x price (~3 cents/video)
- Gemini support is opt-in: needs GEMINI_API_KEY env var to activate

templates/index.html

@@ -267,6 +267,17 @@
         </div>
       </div>
 
+      <div class="row" style="margin-top: 12px;">
+        <div>
+          <label>AI za analizo (popravlja transkript + razume strukturo)</label>
+          <select id="llm-provider">
+            <option value="claude" selected>Claude Sonnet 4.6 (priporočeno)</option>
+            <option value="gemini">Gemini 3.1 Pro (multilingual)</option>
+            <option value="auto">Auto (Claude → Gemini fallback)</option>
+          </select>
+        </div>
+      </div>
+
       <label class="toggle" style="margin-top: 12px;">
         <input type="checkbox" id="no-subs">
         Brez podnapisov
@@ -374,6 +385,7 @@
         subtitle_style: $("#subtitle-style").value,
         quality: $("#quality").value,
         no_subs: $("#no-subs").checked,
+        llm_provider: $("#llm-provider").value,
       };
     }