fix(docker): update compose config and replace Travis with GitHub Actions

[capy-ai]

This PR updates Docker Compose to build the local Finch image instead of pulling the upstream Nitter image, bumps Redis from EOL v6 to v7, removes deprecated docker-compose version key, and replaces the broken Travis CI configuration with a basic GitHub Actions workflow for build verification.

Changes

• docker-compose.yml: Change app service from image: zedeus/nitter:latest to build: . with image: finch:latest, rename container_name from nitter to finch, and update Redis from redis:6-alpine to redis:7-alpine
• docker-compose.yml: Remove deprecated version: "3" key
• .travis.yml: Delete broken Travis CI configuration (Python 3.6, Ubuntu Bionic, insecure Chrome download)
• .github/workflows/ci.yml: Add GitHub Actions workflow to build on push to main and PRs using Nim 2.x, install libsass-dev and pcre, and run nimble build -d:release, nimble scss, nimble md