Deliver Meridian engagement: R1-R4, D2, D3

[federicoterribili]

R1 - Reports remediation:

• Wire location/category/period/status filters to /api/quarterly-reports and /api/monthly-trends; backend accepts all four params
• Fix fulfillment_rate KeyError on 0-order quarters (default to 0)
• Replace hardcoded 'Failed to load reports' error string with i18n key
• Fix hardcoded 'Reports' nav label to use t('nav.reports')

R2 - Restocking Recommendations view:

• New /api/restocking endpoint: priority scoring (high/medium/low), greedy budget ceiling, warehouse/category filters
• New Restocking.vue: budget input, 3 stat cards, 11-col table, reason/priority badges, watches location+category filters
• Add route /restocking and nav link

R3 - Playwright e2e tests:

• tests/e2e/specs/reports.spec.js (9 tests)
• tests/e2e/specs/restocking.spec.js (12 tests)
• Playwright config targeting localhost:3000

R4 - Architecture documentation:

• proposal/architecture.html: layered diagram, component map, API reference, data flow, tech stack overview

D2 - i18n extension:

• Add restocking., backlog., inventoryModal.* keys to en.js + ja.js
• Wire t() calls in Backlog.vue, BacklogDetailModal.vue, InventoryDetailModal.vue (getStockStatus now uses t('status.*'))

D3 - Dark mode:

• useDarkMode composable: toggles .dark on , persists to localStorage
• App.vue: CSS custom properties (:root + .dark overrides) replace all hardcoded colours; sun/moon toggle button in navbar
• FilterBar, LanguageSwitcher, ProfileMenu: scoped styles use var()

Proposal documents (Act 1):

• executive-summary.md, technical-approach.md, relevant-experience.md, timeline.md, pricing.md, capabilities-deck.html, architecture.html