docs: correct drifted counts in CLAUDE.md, declare postcss

The frontend load order omitted session-lineage.js (29 modules listed, 30
loaded), and several inventory counts had drifted from the tree: route handlers
~200 to ~217 with system, files and approvals each understated, src/config 20 to
21 files, install.sh 69KB to 92KB, and the Prettier exemption list, which also
never mentioned mobile.css. Two of the missing handlers are endpoints CLAUDE.md
already documents in prose but never counted.

postcss is imported by two tests but was only present transitively via vite, so
knip reported it as an unlisted dependency. Declared at the version already
resolved in the lockfile.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

package.json

@@ -121,6 +121,7 @@
     "pixelmatch": "^6.0.0",
     "playwright": "^1.58.0",
     "pngjs": "^7.0.0",
+    "postcss": "^8.5.15",
     "prettier": "^3.4.0",
     "puppeteer": "^24.36.0",
     "remotion": "4.0.473",