Remove guideline redirect stubs after one release cycle

## Context

On 2026-06-11, the 20 static HTML pages under `public/guidelines/` were replaced with
minimal meta-refresh redirect stubs as part of the brand-visual migration (Phase 2).

Each stub redirects to the same-named page on the canonical brand-visual Pages site:
`https://crashappsec.github.io/brand-visual/guidelines/.html`

## Action required

One release cycle after this change ships, delete the entire `public/guidelines/` directory
(or replace each stub with a proper HTTP 301 if the hosting layer supports it).

The pages and their redirect targets are:

- animation-guidance.html -> https://crashappsec.github.io/brand-visual/guidelines/animation-guidance.html
- brand-capability-spine.html -> https://crashappsec.github.io/brand-visual/guidelines/brand-capability-spine.html
- brand-icon.html -> https://crashappsec.github.io/brand-visual/guidelines/brand-icon.html
- brand-icons.html -> https://crashappsec.github.io/brand-visual/guidelines/brand-icons.html
- brand-logos.html -> https://crashappsec.github.io/brand-visual/guidelines/brand-logos.html
- color-capabilities.html -> https://crashappsec.github.io/brand-visual/guidelines/color-capabilities.html
- color-neon.html -> https://crashappsec.github.io/brand-visual/guidelines/color-neon.html
- color-neutrals.html -> https://crashappsec.github.io/brand-visual/guidelines/color-neutrals.html
- color-palette.html -> https://crashappsec.github.io/brand-visual/guidelines/color-palette.html
- color-surface-status.html -> https://crashappsec.github.io/brand-visual/guidelines/color-surface-status.html
- diagram-build-lineage.html -> https://crashappsec.github.io/brand-visual/guidelines/diagram-build-lineage.html
- imagery-product-visuals.html -> https://crashappsec.github.io/brand-visual/guidelines/imagery-product-visuals.html
- shadcn-theme.html -> https://crashappsec.github.io/brand-visual/guidelines/shadcn-theme.html
- spacing-radius.html -> https://crashappsec.github.io/brand-visual/guidelines/spacing-radius.html
- spacing-scale.html -> https://crashappsec.github.io/brand-visual/guidelines/spacing-scale.html
- theme-light-dark.html -> https://crashappsec.github.io/brand-visual/guidelines/theme-light-dark.html
- type-body.html -> https://crashappsec.github.io/brand-visual/guidelines/type-body.html
- type-display.html -> https://crashappsec.github.io/brand-visual/guidelines/type-display.html
- type-fonts.html -> https://crashappsec.github.io/brand-visual/guidelines/type-fonts.html
- type-mono.html -> https://crashappsec.github.io/brand-visual/guidelines/type-mono.html