Add 1° download grid layer and download modal

[haithcoatj]

Summary

• Adds a toggleable 1° WGS84 download grid overlay (Global mode only) sourced from the new download-tiles/ftw-download-grid.geojson manifest on Source Cooperative.
• Clicking a grid cell opens a Download Field Data modal showing tile ID, bounding box, feature count, and file size, with a direct link to the per-tile GeoParquet for the year selected in the left panel.
• New composable useDownloadGrid manages layer visibility, hover/selected state, and modal state as singleton state; idempotent per-map init via WeakSet avoids duplicate pointermove listeners across mode switches.

Details

• src/layers/Download-Grid-Layer.ts — vector layer + URL helpers pointing at data.source.coop/ftw/global-field-boundaries/download-tiles/....
• src/composables/useDownloadGrid.ts — visibility/hover/click/modal state; auto-disables when leaving global mode.
• src/components/DownloadModal.vue — Vuetify dialog; uses settings.year (no year picker), disables download + shows warning when the tile has no data for the selected year.
• src/components/GlobalDataPanel.vue — adds the "Download Data" switch.
• src/components/MapComponent.vue / src/composables/useMap.ts — wire click handling to the grid layer and render the modal.
• Tests: src/composables/__tests__/useDownloadGrid.test.ts covers URL builders, featureToGridCell edge cases, singleton state, mode-change auto-disable, and click-gating.

Test plan

• npm run type-check
• npm run lint
• npm run test:unit (12 passing)
• npm run build
• Manual: toggle grid on/off in Global mode, hover highlights, click opens modal, download link resolves, year switch updates modal, disabled state for tiles without data for selected year, grid auto-hides when leaving Global mode.

[m-mohr]

Let's merge after #255 and then see whether we have to align the styling etc.
We also then still have to resolve merge conflicts.

[haithcoatj]

Let's merge after #255 and then see whether we have to align the styling etc. We also then still have to resolve merge conflicts.

Sounds good. Let me know when #255 lands and I'll rebase #256, resolve the conflicts, and do a styling pass.

[m-mohr]

ToDos:

• Whether the download grid is shown or not is not saved in the settings, but in a local ref in the composable.
• Whether the download grid is shown or not is not persisted into the URL.
• When you are zoomed to higher zoom levels, you may actually not see the boxes, the screen only gets a little bluish. Should we zoom out when we enable download so that tiles get shown?
• Hide the explanatory text until downloads are enabled?
• ...

Sometimes random cells are missing?

[Copilot]

Pull request overview

Adds a new “download grid” capability in Global mode, intended to let users identify 1° tiles and download per-tile GeoParquet outputs hosted on Source Cooperative.

Changes:

• Introduces an OpenLayers vector overlay for the 1° download grid plus URL helpers for per-tile GeoParquet downloads.
• Adds settings/permalink support for new downloads toggle and renames fieldBoundariesOpacity → opacity.
• Adds initial UI pieces (Global panel toggle + new DownloadModal.vue) and unit tests for permalink/download-grid helpers.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/layers/Download-Grid-Layer.ts	New OL vector layer sourcing the grid GeoJSON + style and URL helpers.
src/composables/useDownloadGrid.ts	Singleton composable for grid layer init, hover/select state, and click handling.
src/components/DownloadModal.vue	New modal UI intended to show tile metadata and provide a download link.
src/components/GlobalDataPanel.vue	Adds “Download Data” help + toggle; updates opacity binding.
src/components/MapComponent.vue	Wires map singleclick handler; initializes download-grid composable.
src/composables/useMap.ts	Routes clicks to either results selection or download-grid click handler; initializes grid layer in global mode.
src/components/ProcessingResults.vue	Removes per-component map click listener hookup (centralized in MapComponent).
src/composables/useSettings.ts	Renames opacity setting and adds downloads flag with defaults.
src/composables/usePermalink.ts	Adds downloads + opacity to global permalink; refactors parsing/building helpers.
src/composables/tests/useDownloadGrid.test.ts	Unit tests for URL helpers, feature extraction, visibility/mode behavior, and click gating.
src/composables/tests/usePermalink.test.ts	Unit tests for global permalink parts + parsing downloads.

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[m-mohr]

Made various updates, lgtm.

As I'm the last committer, someone else should do another review and approval.