feat: seed the education catalog and a walkable demo planning tree

[AlejandroTatum]

What

Four commits that make a fresh SIGED environment usable end to end, plus one test-harness fix.

• chore: ignore codegraph index — .codegraph/ is a machine-local, per-worktree, regenerable index. Same rule and comment already used in the sibling academic-report-automation repo.
• feat(organizacion): seed educacion niveles catalog — migration 0005 loads the LOEI education levels and subniveles as reference data. EducacionNivel.nombre is unique, so the planificacion model fixture can no longer create Educación General Básica by hand; it now uses a test-scoped name.
• feat(core): seed a walkable planificacion tree in seed_demo — seed_demo stopped at users, instituciones and roles, so there was no plan de estudio to open. It now builds one active plan with grados and asignaturas, and scripts/dev.sh runs it during backend bootstrap.
• test(frontend): install an in-memory storage fallback in the vitest setup — Node 26's experimental global localStorage stays undefined without --localstorage-file, and under jsdom it shadows the jsdom storage.

Notes on the split

The migration and seed_demo are separate commits on purpose: the catalog is production reference data that runs on every deploy, while seed_demo is dev-only demo data guarded behind DEBUG. The test_planificacion_models.py fixture rename ships with the migration because the unique constraint forces it — without the rename that test fails the moment 0005 is applied.

test_seed_catalogo.py is split across both commits so each one carries its own tests: the catalog assertions land with the migration, the seed_demo assertions with the command.

Demonstrating RF-017

The seeded grados are chosen so the weekly-minimum alert is visible both ways — 4to de Básica meets its Básica Elemental minimum, 8vo de Básica deliberately falls short of Básica Superior and raises the alert. test_seeds_one_grado_that_meets_its_minimum_and_one_that_does_not locks that in.

Verification

Check	Result
python -m pytest (backend, --create-db)	116 passed
npm test (frontend, vitest)	153 passed, 24 files
manage.py makemigrations --check --dry-run	No changes detected
Migration 0005 on a fresh database	Applies cleanly; depends on existing 0004, no numbering conflict
Commit 189bbea in isolation	111 passed — the branch bisects clean