Show top contributor heatmap in README for vector and vrl

Promotes the generated heatmap PNGs to data/images/ and references
them at the end of each repo's Pull Requests section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: pront

README.md

@@ -155,6 +155,10 @@ Audit logs written to `out/purge/` (local only).
 
 ![Top Integration PRs By Label Total Count](data/images/vectordotdev_vector_pull_requests.open_closed_total_label_count.png)
 
+---
+
+![Top 10 PR Contributors (last 12 months)](data/images/vectordotdev_vector_pull_requests.contributors_top10_12m.png)
+
 ##### Discussions
 
 ![Monthly Discussions](data/images/vectordotdev_vector_discussions.monthly_trend.png)
@@ -187,6 +191,10 @@ Audit logs written to `out/purge/` (local only).
 
 ![PR Label Counts](data/images/vectordotdev_vrl_pull_requests.label_counts.png)
 
+---
+
+![Top 10 PR Contributors (last 12 months)](data/images/vectordotdev_vrl_pull_requests.contributors_top10_12m.png)
+
 ##### Discussions
 
 ![Monthly Discussions](data/images/vectordotdev_vrl_discussions.monthly_trend.png)