fix(workflow): use GitHub Releases + Docker Hub hybrid for version detection

Root cause: Docker Hub sorts tags by last_updated (non-monotonic).
Some versions (e.g. 2.24.x) had older last_updated than 2.23.4, so they
fell off page 1 and were never detected. Workflow stuck at 2.22.2.

Fix:
- Primary source: GitHub Releases API (stable releases, per_page=30)
- Secondary source: Docker Hub page 1 (catches releases before GitHub promotes them)
- Take the maximum of both candidates
- Sanity check: LATEST must be >= CURRENT to prevent false downgrades
- Added --retry 3 and .draft==false filter to GitHub source

Also bump chart and image to 2.26.3 (manual catch-up from 2.22.2).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Chart.yaml

@@ -2,8 +2,8 @@ apiVersion: v2
 name: n8n
 description: A Helm chart for n8n workflow automation on Kubernetes (ARM/Raspberry Pi ready)
 type: application
-version: "2.22.2"
-appVersion: "2.22.2"
+version: "2.26.3"
+appVersion: "2.26.3"
 keywords:
   - n8n
   - workflow