chore: switch from develop/dev to main/latest image tags

Remove develop branch references from CI, compose, env, and docs
now that all development uses trunk-based workflow on main.

- CI: remove develop branch filters and dev tag logic
- Compose: default IMAGE_TAG from dev to latest
- Env: update IMAGE_TAG default and comments
- Docs: update branching strategy, PR targets, and image tag docs

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

docs/SWARM-DEPLOYMENT.md

@@ -49,7 +49,7 @@ nano .env
 - `OIDC_CLIENT_ID` - From your Authentik/OIDC provider
 - `OIDC_CLIENT_SECRET` - From your Authentik/OIDC provider
 - `OIDC_ISSUER` - Your OIDC provider URL (must end with `/`)
-- `IMAGE_TAG` - `dev` or `latest` or specific commit SHA
+- `IMAGE_TAG` - `latest` (default) or specific version/commit SHA
 
 ### 2. Configure for External Services (Optional)
 
@@ -131,10 +131,10 @@ See [OpenBao Deployment Guide](OPENBAO-DEPLOYMENT.md) for detailed options.
 cd /opt/mosaic/stack
 
 # Using the deploy script (recommended)
-IMAGE_TAG=dev ./scripts/deploy-swarm.sh mosaic
+IMAGE_TAG=latest ./scripts/deploy-swarm.sh mosaic
 
 # Or manually
-IMAGE_TAG=dev docker stack deploy \
+IMAGE_TAG=latest docker stack deploy \
   -c docker-compose.swarm.yml \
   --with-registry-auth mosaic
 ```