[ANAMASGARD]

Fixes #55.

• Adds an optional sowing density field (plants/m²) so users can record how densely each crop was sown, alongside or instead of seed weight.

• The field uses the existing schema-driven form and accepts zero and fractional values. Both measurements remain optional, and existing records continue to work.

• Regression tests cover validation, editing, persistence, and CSV/JSON exports. Local testing completed with 291 passing assertions.

Verification

• 291 passing assertions, with one existing test skipped.
• Browser checks confirmed validation, saving, reopening, editing, and CSV/JSON exports.
• Package check completed with zero errors; existing warnings and note were reproduced on the unchanged baseline.

Screenshot

Reopened sowing event showing zero, blank, and fractional density values for different crops.