Build with Podman and deploy as a rootless Quadlet on emily

- Makefile: podman build/push from the committed tree (git archive HEAD),
  tagged :<commit> + :latest; PLATFORM defaults to linux/arm64 for emily.
- deploy.sh: push the commit first, refuse a dirty tracked tree or
  HEAD != origin/main, then build and deploy that exact commit via
  -e image_tag (rollback = an older commit).
- ansible: target emily with no become. The register role writes hops.network
  (NetworkName=hops_net) plus the caddy.container.d drop-in; the hops role
  installs ~/podman-data/hops and hops.container under systemctl --user with a
  podman healthcheck gate; the caddy role appends the site blocks to the shared
  Caddyfile and reloads.
- Drop the Docker-era network role, community.docker requirements,
  ansible/files templates and docker-compose.yml.
- .containerignore replaces .dockerignore.
- README: Podman build, rootless Quadlet deploy on emily.

.dockerignore

@@ -1,40 +0,0 @@
-# Version control & IDEs
-.git
-.gitignore
-.dockerignore
-.vscode
-.idea
-.agents
-.gemini
-
-# Build artifacts & compiled outputs
-.output
-frontend/.output
-frontend/.tanstack
-frontend/dist
-dist
-
-# Dependencies
-node_modules
-frontend/node_modules
-
-# PocketBase local data & local binaries
-backend/pb_data
-backend/pocketbase
-backend/pocketbase.exe
-*.db
-*.db-shm
-*.db-wal
-
-# Logs & temporary files
-*.log
-npm-debug.log*
-scratch
-page.html
-.DS_Store
-Thumbs.db
-
-# Documentation
-README.md
-walkthrough.md
-implementation_plan.md