feat(#59): add weekly training planner view

[ChristopherRotnes]

Summary

• New Planlegger view lets the user assign session templates to days of the current week and see projected muscle coverage on a live heatmap body map before training starts
• Addresses the gap where every other screen answers "what did I do?" — this one answers "what should I do next?"
• Closes As a user I want to plan my training week upfront so I can see projected muscle coverage before I start #59

Changes

Supabase migration

• week_plans — one row per user per ISO week, RLS enforced
• week_plan_days — one row per day slot, cascades on plan delete, RLS via parent join

utils.js

• toWeekIso(date) — Date → "2026-W19", handles ISO week year-rollover edge cases
• weekIsoToMonday(weekIso) — "2026-W19" → Monday Date

db.js

• fetchWeekPlan(weekIso) — fetches plan + days with joined template data
• saveWeekPlan(weekIso, assignments) — upserts plan row, delete + reinserts days
• deleteWeekPlan(weekIso) — deletes plan row (cascade removes days)

Planlegger.jsx (new component)

• Week navigation (ChevronLeft/ChevronRight) with UKE N · D–D MÅNED label
• HeatmapBodySVG projected coverage map, updates live as templates are assigned
• Forslag card surfaces when ≥2 muscle groups are uncovered, lists up to 3 matching templates
• 7-day row list — assigned rows show template name + muscle AccentChips + remove button; empty rows show dashed + Legg til økt
• Bottom-sheet template picker overlay, closes on Escape or backdrop click
• Sticky CTA: Fjern uke (ghost, only when a saved plan exists) + Lagre plan (primary)
• Confirm-delete strip before deletion executes
• Mobile: Front/Bak toggle on body map

App.jsx — Planlegger import, onShowPlanlegger in NavContext, "planlegger" view branch

PageShell.jsx — EventSchedule Carbon icon nav button (between Bibliotek and theme toggle)

Verification steps

1. SQL migration ran; RLS blocks cross-user access
2. EventSchedule calendar icon in nav → navigates to Planlegger, shows current week
3. ChevronLeft/ChevronRight update week label and reload plan correctly
4. Assign a template to a day → HeatmapBodySVG updates live
5. ≥2 muscle groups uncovered → Forslag card appears; cover them all → card disappears
6. Lagre plan → rows persisted in Supabase; reload page → plan loads back
7. Fjern uke → confirm strip appears → confirm → week_plans row deleted (cascade removes days)
8. Mobile: Front/Bak toggle works, bottom-sheet template picker opens and closes
9. Unit tests for toWeekIso / weekIsoToMonday at year rollover (29 Dec → W01 next year)

Out of scope

• Drag-and-drop day reordering
• Multi-week arc / program builder
• Converting a saved plan into a logged session directly from this view

https://claude.ai/code/session_01XVey99eDCo79X8b6fNQuKP

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