fix(deps): scope the vite < 7 override to vitepress so @angular/build keeps vite 8

The unconditional `"vite": ">=6.4.2 <7"` override added in #161 to
keep VitePress 1.x off rolldown-vite (vite 7+) had the side effect
of downgrading **every** vite consumer in the workspace to vite
6.4.2 — including `@angular/build@21.2.11`, whose internal
`angular-memory-plugin.js > loadViteClientCode` monkey-patches the
Vite client error-overlay code. The patch targets vite 8.x's
internal layout; against vite 6 it throws:

  [vite] Internal server error: Failed to update Vite client error
  overlay text.
    at loadViteClientCode (angular-memory-plugin.js:140:31)

…on the very first request to `pnpm nx serve portal-shell`. The
shell renders a blank screen until the workspace's vite is back to
8.x.

Fix: scope the override to vitepress's transitive resolution only,
using pnpm's `parent>child` selector syntax. Diff is one line:

-  "vite":          ">=6.4.2 <7",
+  "vitepress>vite": ">=6.4.2 <7",

Post-fix resolutions (verified against pnpm-lock):
  - VitePress → vite@6.4.2 (Rollup-based, VitePress 1.x compatible)
  - @angular/build, @nx/vite, Vitest, etc. → vite@8.0.13 (restored)
  - @vitejs/plugin-basic-ssl (analog dep) → vite@7.3.2 (its own
    peer range; not the patched-7+ rolldown branch in a way that
    affects us — it's used for HTTPS-cert generation only, not
    dev-server hosting).

Verification:
  * `pnpm audit --audit-level=moderate` → no known vulnerabilities.
  * `pnpm docs:build` → 9.5 s, Mermaid still renders in ADR-0009.
  * `pnpm nx run-many -t lint test build` on the 6 main projects
    → all green.
  * `pnpm nx serve portal-shell` → boots cleanly, HTTP 200 on
    `/`, no `loadViteClientCode` error in the dev log.

package.json

@@ -44,7 +44,7 @@
       "ip-address@<10.1.1": ">=10.1.1",
       "protobufjs@<8.0.2": ">=8.0.2",
       "tmp@<0.2.4": ">=0.2.4",
-      "vite": ">=6.4.2 <7",
+      "vitepress>vite": ">=6.4.2 <7",
       "yaml@<2.8.3": ">=2.8.3",
       "@types/express": "^5.0.6"
     }