Stabilize modal rendering and sequential Gemini flow

TODO.md

@@ -255,6 +255,22 @@
   - backend debug broadcasts
 
 ## Recent Change Log
+- Date: `2026-03-16`
+- What changed:
+  - Search enrichment now runs across the full result set sequentially instead of only enriching a capped top subset in parallel.
+  - Gemini Vision evaluation now runs candidate-by-candidate with retries and delay, and fallback-only / clearly negative items are excluded from final output.
+  - Result modal now uses YouTube embed only for Google Video and falls back to source preview video or thumbnail for Envato / Artgrid, avoiding iframe refusal for blocked providers.
+  - When `GEMINI_API_KEY` is absent, the API still returns ranked fallback results so local smoke tests and non-Gemini environments stay usable.
+- Why it changed:
+  - The user preferred reliability over speed and wanted all candidates processed thoroughly.
+  - Negative or irrelevant Gemini outcomes were still leaking into the final result set.
+  - Envato iframe embeds were being blocked, and Google Video modal opening was broken by missing frontend YouTube ID extraction.
+- How it was verified:
+  - code inspection of sequential search/enrichment/evaluation flow
+- What is still risky or incomplete:
+  - Fully sequential Gemini and enrichment processing increases search latency noticeably.
+  - Some Envato / Artgrid items may still only have thumbnails if public preview URLs are not exposed in source metadata.
+
 - Date: `2026-03-16`
 - What changed:
   - Result modal layout was rebuilt to match a top `16:9` embedded viewer with bottom-left full AI note and bottom-right action panel.