refactor: share viz footer assets across R and Python

[cpsievert]

Stacked on #224.

Summary

Centralize the visualization footer assets under js/ and generate the package-local artifacts for both runtimes from a single shared source.

This branch now does four concrete things:

• adds a minimal shared web asset toolchain under js/ and copies generated viz.js / viz.css into pkg-r and pkg-py
• extracts the common footer behavior into viz-core.ts and makes web-build atomic while making web-check fail on stale generated assets
• unifies the runtime contract so both R and Python write the final DOM id into the footer and both export through Vega Embed's action links
• trims diff and runtime noise by preserving the original CSS ordering and simplifying footer click handling to a single action lookup plus tracked open-menu state

The browser-side result is that the shared logic now owns:

• query toggle behavior
• save menu open/close behavior
• outside-click closing
• PNG/SVG export through a shared Vega action-link path

The runtime-specific surface is much smaller than where this branch started.

Verification

• make web-build
• make web-check
• Rscript -e "devtools::test('pkg-r', filter = '^(viz-tool|querychat-viz)$', reporter = 'summary')"
• uv run pytest pkg-py/tests/test_viz_footer.py -v
• uv run pytest pkg-py/tests/playwright/test_11_viz_footer.py -k 'click_save_opens_menu or click_outside_closes_menu or toggle_save_menu' -v
• uv run pytest pkg-py/tests/playwright/test_11_viz_footer.py -k 'save_as_png_downloads_png or save_as_svg_downloads_svg' -v
• Live R module repro via Playwright confirmed namespaced-id save menu behavior and successful Repro Chart.png / Repro Chart.svg downloads

[Copilot]

Pull request overview

Centralizes the visualization footer JS/CSS into a shared js/ source, then generates package-local artifacts for both the R and Python runtimes. This reduces divergence between implementations and adds stronger guarantees that committed web assets match the sources.

Changes:

• Introduce shared js/src/viz-core.ts + thin runtime entrypoints and generate viz.js/viz.css into pkg-r and pkg-py.
• Update R/Python footer markup to use data-querychat-action and resolve Shiny DOM widget IDs for export behavior.
• Add web-build/web-check targets and Playwright coverage for “Save as PNG/SVG” downloads in Python.

Reviewed changes

Copilot reviewed 17 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg-r/inst/htmldep/viz.js	Replace inline footer logic with generated bundle sourced from shared viz-core.
pkg-r/inst/htmldep/viz.css	Add generated-file header; CSS now sourced from shared js/src/viz.css.
pkg-r/R/querychat_viz.R	Add data-querychat-action attributes and ensure DOM widget ID is passed for exports.
pkg-py/src/querychat/static/js/viz.js	Replace runtime-specific implementation with generated bundle sourced from shared viz-core.
pkg-py/src/querychat/static/css/viz.css	Add generated-file header; keep in sync with shared CSS source.
pkg-py/src/querychat/_viz_tools.py	Resolve Shiny DOM widget IDs via resolve_id; add data-querychat-action attributes in footer markup.
pkg-py/tests/test_viz_footer.py	Add unit tests asserting resolved DOM widget IDs are used in rendered footer markup.
pkg-py/tests/playwright/test_11_viz_footer.py	Add real download assertions for PNG/SVG export via the Save menu.
js/src/viz-core.ts	New shared footer event delegation + export adapter interface.
js/src/viz-r.ts	New R entrypoint wiring shared core + Vega action adapter.
js/src/viz-py.ts	New Python entrypoint wiring shared core + Vega action adapter.
js/src/viz.css	New shared CSS source for viz container/footer styling.
js/build.mjs	New build pipeline to stage and copy generated assets into R/Python package locations.
js/check.mjs	New “stale output” check to fail when committed generated assets diverge from sources.
js/package.json	New private JS workspace for shared asset build/check scripts.
js/package-lock.json	Lockfile for shared JS tooling (esbuild, typescript).
js/tsconfig.json	New TS config for typechecking shared sources (no emit).
Makefile	Add web-setup, web-build, web-check targets for shared asset workflows.
.gitignore	Ignore js/node_modules/.

Files not reviewed (1)

• js/package-lock.json: Language not supported

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