feat: allow selecting multiple categories in demographic filters

[Joe-Heffer-Shef]

Summary

The survey report's demographic data filters used single-value dropdowns, so users could only filter to one category at a time. This converts categorical filters to checkbox lists, so multiple categories can be selected at once (e.g. several hospital sites within a Trust).

Screenshots

Each demographics field has a multi-checkbox option like this:

The selected categories are shown below the filter panel

The charts are all filtered based on the selected categories

Changes — SurveyDemographicFilters.svelte

• State: Categorical filters now hold a string[] of selected options (empty = "All") instead of a single value. Types and onMount initialisation updated accordingly.
• Filter logic: A response is kept if its value is in the selected set (includes); an empty selection applies no filtering. Numeric range filters are unchanged.
• Active filters display: Multiple selections render comma-joined (e.g. Royal Hallamshire, Northern General). FilterAlert.svelte already renders this as free text, so it needed no change.
• Clear filters: Resets categorical filters to a fresh empty array.
• Markup: Replaced the <select> with an accessible checkbox group — <fieldset>/<legend> for grouping and for/id-linked labels (per the repo's WCAG focus), using Bootstrap form-check classes. Added a toggleOption helper that reassigns the array so Svelte 5 runes reactivity fires.

Tests

Added three tests: checkboxes render (no <select>), ticking two options keeps the union and shows both in the active filter, and an empty selection passes all responses through. The existing disabled-field regression test still passes.

Verification

• npx vitest run on the suite: 4 passed.
• npx eslint on both changed files: clean.

The backend (survey/views.py, survey/models.py) needed no changes since all filtering is client-side, and exports operate on the filtered set already passed through these components.

Closes #605

🤖 Generated with Claude Code

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	21.33%	584 / 2737
🔵	Statements	21.33%	584 / 2737
🔵	Functions	28.72%	27 / 94
🔵	Branches	63.93%	117 / 183

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
ui_components/src/lib/components/SurveyDemographicFilters.svelte	90.1%	76.78%	83.33%	90.1%	130-132, 165-169, 193-194, 220-230

Generated in workflow #327 for commit ba2b868 by the Vitest Coverage Report Action

[Joe-Heffer-Shef]

Closes #605