chore(scripts): harden upload-assets for monorepo + symlink edge cases

[wab]

Two pre-existing hardening notes from the PR #48 review, neither blocking today:

1. getChangedAssets assumes posts/ is its own git root

scripts/upload-assets.js#getChangedAssets runs git ls-files with cwd: rootDir and compares against relative(rootDir, …). Works because this repo is its own git root, but would silently filter everything out if the repo ever became a subdir of a larger checkout (e.g. monorepo).

Fix: call git rev-parse --show-toplevel and use that as the base for path resolution instead of rootDir.

2. findAssetFiles follows symlinks

scripts/upload-assets.js#findAssetFiles uses stat (which follows symlinks) rather than lstat. Not a concern for current content but would silently traverse outside assets/ if a symlink ever appeared.

Fix: swap to lstat, skip symlinks (or refuse with a clear error if isSymbolicLink()).

Acceptance

• Both behaviours covered by tests in scripts/__tests__/upload-assets.test.js
• No behavioural change for the current repo layout (assertion: pnpm upload-assets:migrate still finds 141 files)

[wab]

This was generated by AI during triage.

Two hardening notes raised during PR #48 code review, not blocking today's behaviour but worth fixing before the repo ever lives in a monorepo or sees symlinked assets.

My recommendation: enhancement + ready-for-agent. Reason: scoped, behaviour-neutral for current layout, has explicit acceptance (existing test count + behavioural assertion). Body already reads like an agent brief — but maintainer should verify it's durable before any agent picks it up.