fix(landing): add valid pnpm-workspace.yaml (packages + build approvals)

Host cochi carried an untracked landing/pnpm-workspace.yaml with a bogus
`allowBuilds:` key and no `packages:` field, which made pnpm 11 abort every
command with "packages field missing or empty" — breaking the deploy landing
rebuild. Track a correct file: `packages: ['.']` plus `onlyBuiltDependencies`
for esbuild/sharp. Verified install + astro build clean locally.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

landing/pnpm-workspace.yaml

@@ -0,0 +1,5 @@
+packages:
+  - '.'
+onlyBuiltDependencies:
+  - esbuild
+  - sharp