fix(app): decision modal layout, attachments and mobile-safe forms

[gnacho]

Closes #284

Decision modal readability and mobile fixes:

• Solution cards: vote beside the edit button on the title row; text gets full width; the choose button floats on the author line (accent color, creator/admin only, no separator).
• Attachments are only visible while editing: description attachments in description edit mode, solution attachments while editing that solution. Upload/download/delete controls no longer steal focus from the editing textarea.
• Shared action row: propose, close and delete sit together on one row; the comment form stacks the submit button below the input so narrow screens do not overflow.
• Closed decisions: short "Close" label with armed double confirmation and a neutral confirmation message (the "may not be the most voted" note stays only on the choose dialog).
• Task comments tab uses the same stacked comment form.

Frontend only (DecisionModal.tsx, task/CommentsTab.tsx, i18n es/en). No server changes.