Phase 5: per-child dashboard (overdue first), item detail, delete

- internal/dashboard: classify items into overdue / due today / due this week /
  no due date / messages; render the plain-text brief (FR-6, FR-7, FR-9).
- internal/store: ItemsForChild, ItemByID, DeleteItemByID, ScanSummaryForChild
  and the stored-brief CRUD helpers (FR-10).
- internal/web: routes /?child=, /items/{id}, POST /items/{id}/delete,
  POST /summaries/build, POST /summaries/{id}/delete, plus a per-child scan
  banner (FR-12) and a phone-first server-rendered template.
- Calendar events are never "overdue": a past lesson is history, not work.
- cmd/school brief build|list; scripts/screenshot-phase5.mjs for phone evidence.
- Tests: bucket classification, stored-brief round-trip, and HTTP routes
  including the NO SCAN / SCAN FAILED / healthy banner behaviour.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Makefile

@@ -1,5 +1,5 @@
-IMAGE ?= compass-teams-nhs/school:0.3.0-phase4
-BUILD_VERSION ?= 0.3.0-phase4
+IMAGE ?= compass-teams-nhs/school:0.3.0-phase5
+BUILD_VERSION ?= 0.3.0-phase5
 
 # Parse options (see scripts/parse-compass.sh).
 CHILD ?= Harry