fix: declare @tailwindcss/postcss in admin/space/web for Docker builds (#9189)

The web/admin/space Docker image builds fail at the Vite/PostCSS step with
"Cannot find module '@tailwindcss/postcss'". These apps load the shared
@plane/tailwind-config/postcss.config.js, which references the @tailwindcss/postcss
plugin by name, but the plugin was only declared as a dependency of
packages/tailwind-config.

The Docker build installs via turbo prune + 'pnpm fetch' + 'pnpm install --offline',
which lays out node_modules so PostCSS resolves the plugin relative to the app
directory (apps/<app>), where it is not reachable. A plain 'pnpm install' resolves
it from tailwind-config's context instead, which is why local builds passed and
masked the issue.

Declare @tailwindcss/postcss as a direct devDependency of the three apps that run
Vite/PostCSS so it is symlinked into each app's node_modules and resolves under the
isolated linker regardless of install flow.

Verified by reproducing the exact Docker flow (prune -> fetch -> --frozen-lockfile
offline install -> build) for admin, space and web: all install in sync and build
successfully with full Tailwind CSS output.

apps/admin/package.json

@@ -52,6 +52,7 @@
     "@plane/tailwind-config": "workspace:*",
     "@plane/typescript-config": "workspace:*",
     "@react-router/dev": "catalog:",
+    "@tailwindcss/postcss": "catalog:",
     "@types/lodash-es": "catalog:",
     "@types/node": "catalog:",
     "@types/react": "catalog:",

apps/space/package.json

@@ -56,6 +56,7 @@
     "@plane/tailwind-config": "workspace:*",
     "@plane/typescript-config": "workspace:*",
     "@react-router/dev": "catalog:",
+    "@tailwindcss/postcss": "catalog:",
     "@tailwindcss/typography": "catalog:",
     "@types/lodash-es": "catalog:",
     "@types/node": "catalog:",

apps/web/package.json

@@ -76,6 +76,7 @@
     "@plane/tailwind-config": "workspace:*",
     "@plane/typescript-config": "workspace:*",
     "@react-router/dev": "catalog:",
+    "@tailwindcss/postcss": "catalog:",
     "@tailwindcss/typography": "catalog:",
     "@types/lodash-es": "catalog:",
     "@types/node": "catalog:",

pnpm-lock.yaml

@@ -706,6 +706,9 @@ importers:
       '@react-router/dev':
         specifier: 'catalog:'
         version: 7.13.1(@react-router/serve@7.13.1(react-router@7.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(typescript@5.8.3))(@types/node@22.12.0)(jiti@2.6.1)(lightningcss@1.30.2)(react-router@7.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(terser@5.43.1)(tsx@4.20.6)(typescript@5.8.3)(vite@7.3.2(@types/node@22.12.0)(jiti@2.6.1)(lightningcss@1.30.2)(terser@5.43.1)(tsx@4.20.6)(yaml@2.8.3))(yaml@2.8.3)
+      '@tailwindcss/postcss':
+        specifier: 'catalog:'
+        version: 4.1.17
       '@types/lodash-es':
         specifier: 'catalog:'
         version: 4.17.12
@@ -993,6 +996,9 @@ importers:
       '@react-router/dev':
         specifier: 'catalog:'
         version: 7.13.1(@react-router/serve@7.13.1(react-router@7.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(typescript@5.8.3))(@types/node@22.12.0)(jiti@2.6.1)(lightningcss@1.30.2)(react-router@7.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(terser@5.43.1)(tsx@4.20.6)(typescript@5.8.3)(vite@7.3.2(@types/node@22.12.0)(jiti@2.6.1)(lightningcss@1.30.2)(terser@5.43.1)(tsx@4.20.6)(yaml@2.8.3))(yaml@2.8.3)
+      '@tailwindcss/postcss':
+        specifier: 'catalog:'
+        version: 4.1.17
       '@tailwindcss/typography':
         specifier: 'catalog:'
         version: 0.5.19
@@ -1195,6 +1201,9 @@ importers:
       '@react-router/dev':
         specifier: 'catalog:'
         version: 7.13.1(@react-router/serve@7.13.1(react-router@7.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(typescript@5.8.3))(@types/node@22.12.0)(jiti@2.6.1)(lightningcss@1.30.2)(react-router@7.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(terser@5.43.1)(tsx@4.20.6)(typescript@5.8.3)(vite@7.3.2(@types/node@22.12.0)(jiti@2.6.1)(lightningcss@1.30.2)(terser@5.43.1)(tsx@4.20.6)(yaml@2.8.3))(yaml@2.8.3)
+      '@tailwindcss/postcss':
+        specifier: 'catalog:'
+        version: 4.1.17
       '@tailwindcss/typography':
         specifier: 'catalog:'
         version: 0.5.19