Switch to master branch + Gitea Actions

- Move CI/release workflows from .github/workflows to .gitea/workflows (Gitea Actions),
  targeting the master branch.
- docker-publish: push to the Gitea container registry (git.finalfactory.de) with a
  lowercased image name; login via github.token or a PACKAGES_TOKEN secret.
- version-tag: gitea-actions bot identity; optional RELEASE_TOKEN to re-trigger the image build.
- Update README/CLAUDE.md/Unraid template/build-and-push.ps1 to the Gitea registry + master.

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

deploy/unraid-template.xml

@@ -4,15 +4,15 @@
      separately, or point ConnectionStrings__Default at an existing instance). -->
 <Container version="2">
   <Name>MeterVault</Name>
-  <Repository>ghcr.io/finalfactory/metervault:latest</Repository>
-  <Registry>https://ghcr.io/finalfactory/metervault</Registry>
+  <Repository>git.finalfactory.de/finalfactory/metervault:latest</Repository>
+  <Registry>https://git.finalfactory.de/FinalFactory/-/packages/container/metervault</Registry>
   <Network>bridge</Network>
   <Shell>bash</Shell>
   <Privileged>false</Privileged>
   <Overview>Self-hosted energy &amp; utility metering: ingest from Home Assistant/Tasmota/MQTT, normalize to consumption, and produce cost dashboards. Needs a TimescaleDB instance.</Overview>
   <Category>HomeAutomation: Tools: Productivity:</Category>
   <WebUI>http://[IP]:[PORT:8080]/</WebUI>
-  <Icon>https://raw.githubusercontent.com/FinalFactory/MeterVault/main/docs/icon.png</Icon>
+  <Icon>https://git.finalfactory.de/FinalFactory/MeterVault/raw/branch/master/docs/icon.png</Icon>
 
   <Config Name="WebUI Port" Target="8080" Default="8080" Mode="tcp" Description="HTTP port" Type="Port" Display="always" Required="true">8080</Config>