Add sensors to filters and add other missing filters

[gosku]

Summary

• Add missing numeric filters (highlight, shadow, color, sharpness, high_iso_nr, clarity) to the recipes explorer sidebar. These were stored as DecimalField in the DB but missing from RECIPE_FILTER_FIELDS; a fix to the is_numeric check ensures correct null exclusion and numeric sort order for decimal values.
• Add a sensor filter to both the recipes explorer and images gallery sidebars. Sensors are a M2M relation and required special-casing: faceted counts use distinct=True, and the gallery filter applies the M2M lookup via a pk-subquery to avoid corrupting the Count("images") annotation. Recipes with no sensor assigned show as "Not assigned" (URL value: none).
• Sensor filter appears immediately below Film Simulation in both sidebars.

Notes

• RECIPE_FILTER_FIELDS was intentionally left unchanged — sensors are handled as a special case in the filter functions rather than as a simple field lookup.
• Both view helpers (_active_filters_from_request, _recipe_explorer_filters_from_request) were updated to read sensors from the request, since it is not covered by the RECIPE_FILTER_FIELDS loop.
• The sidebar templates now use {{ option.label|default:option.value }} to allow a display label that differs from the URL parameter value.