feat: add Docker environment for parser demo and tests

[egorsmkv]

Add a multi-stage Dockerfile that installs the Rust/native prerequisites, builds the existing quotes_spider with Cargo.lock and runs the compiled parser as UID/GID 10001 in a Debian Bookworm runtime. The default offline mode follows two local fixture pages and exports three quotes to /app/data/quotes.jl. Add an optional test target with compiler/source and the repository/skill/offline example checks.

Add .dockerignore, container documentation, an exact JSONL output checker and a path-filtered CI workflow. CI builds the runtime image, executes with --network none, checks output and confirms the configured non-root user. No image publishing.

Validation completed: local existing quotes_spider binary parsed both fixture pages and produced all three expected items; output checker rejected invalid output; Dockerfile structure and workflow YAML parsed; bash syntax, formatting, documentation links and diff whitespace checks passed.

Limitation: this environment has neither Docker nor Podman installed, so an actual image build/container run could not be performed locally. The added CI smoke job performs that verification. Base images and native package downloads require network during build; optional test-feature dependencies may also be fetched during test-image execution.