Docente drill-down: /alumnos practica count linked to a filtered /practicas view

SHIPPED ed6bd3c 0.24.23, filed for the record rather than as pending work. /alumnos showed a per-alumno practica count with no route to the practicas themselves, and /practicas filtered by modulo only, so a docente reading "5 practicas cargadas" had nowhere to click. Added ?alumno=<uuid> to /practicas, composing with ?modulo in both directions, and made the count a link when it is non-zero. Three decisions worth keeping: the uuid is REGEX-VALIDATED before it reaches the query because an arbitrary string in a uuid comparison raises 22P02 and 500s the page, unlike the int modulo id which coerces harmlessly; the alumno NAME for the heading is a separate query rather than rows[0] so a filter matching nobody still renders as "this alumno has no practicas" instead of collapsing into "no practicas exist"; a zero count is plain text, not a link, because a link to an empty list reads as broken rather than as accurate. UNEXERCISED: zero practicas exist in terra, so every path here has run against an empty table only.