fix(brand): solid xxllnc tokens, fix typos, MDI app icons, remove dead assets

[rubenvdlinde]

Summary

• [HIGH] xxllnc token set ships translucent primary color (#000000ad) — fails brand rules and WCAG #118 (HIGH) — xxllnc primary/hover were translucent (#000000ad/#00000080); replaced with solid #000000/#333333 to comply with brand solid-colour rule and guarantee WCAG AA contrast on any background. Comment added to flag upstream xxllnc maintainers.
• [HIGH] xxllnc typo --nldesign-color-succes silently leaves success color undefined #119 (HIGH) — Typo --nldesign-color-succes (missing 's') left success colour undefined in the xxllnc set. Corrected to --nldesign-color-success in both the nldesign and xxllnc palette sections. Same fix for alert-succes variants.
• [MEDIUM] Brand drift: legacy cobalt #4376FC in docs/static/img/logo.svg #120 (MEDIUM) — docs/static/img/logo.svg used legacy cobalt #4376FC; replaced with canonical #21468B (Dutch flag blue, retired 2026-05-13).
• [MEDIUM] App icons use translucent fill (opacity=0.3) — violates brand solid-colours rule #121 (MEDIUM) — All three app icon files contained opacity="0.3" rect violating solid-colours brand rule; replaced with proper MDI palette-swatch glyph: fill="#fff" 24×24 for app.svg, no-fill for app-dark.svg, #21468B hexagon + white glyph for app-store.svg.
• [MEDIUM] Duplicate Fira Sans font files in css/fonts/ — unreferenced dead weight #124 (MEDIUM) — css/fonts/ was an unreferenced duplicate of css/systems/nldesign/fonts/; deleted all 8 font files (~2 MB dead weight). No stylesheet references this directory.
• [MEDIUM] nederland-logo.svg and nederland-map.svg are byte-identical; -backup file present #125 (MEDIUM) — nederland-logo.svg and nederland-map.svg were byte-identical (confirmed md5); only nederland-logo.svg is referenced (rijkshuisstijl.css line 89); deleted duplicate nederland-map.svg and stale nederland-map-backup.svg.

Test plan

• Verify xxllnc token set shows solid black primary colour (no translucency)
• Verify xxllnc success alerts/banners now render correctly (was undefined due to typo)
• Verify docs site logo shows #21468B cobalt (not the old #4376FC)
• Verify app icons display correctly in Nextcloud app list (no empty/translucent squares)
• Verify fonts still load correctly (Fira Sans from css/systems/nldesign/fonts/)
• Verify Rijkshuisstijl logo still loads (references nederland-logo.svg which is kept)