docs(nh3-dev): Playwright/Chromium is box-wide, not lkraven-only

Reflects the shared install: browsers in /opt/ms-playwright (root-owned,
world-readable) + PLAYWRIGHT_BROWSERS_PATH wired globally via
/etc/environment + profile.d, so any user/project resolves the shared
binary without a per-home playwright install. Includes the add-a-browser
command for future bumps.

servers/nh3-dev/README.md

@@ -23,9 +23,21 @@ local Bash already executes here — no SSH-to-self needed for non-privileged wo
 - **volva** — Codex peer agent on the althing bus (single-turn oracle, systemd
   daemon).
 - **bloom_music dev** — `~/development/bloom_music`; its `web/` test harness uses
-  Playwright headless Chromium. System deps + the managed Chromium binary
-  (`~/.cache/ms-playwright`) installed 2026-06-04 via `infra-ops`; headless launch +
-  real SVG geometry verified.
+  Playwright headless Chromium for OSMD browser-geometry assertions.
+
+## Box-wide Playwright / Chromium (2026-06-04)
+
+Available to **every user/project** on this box — no per-home `playwright install`:
+- System shared-libs: apt-installed via `playwright install-deps chromium` (Debian-12
+  set + xvfb), global.
+- Browser binaries: **shared `/opt/ms-playwright`** (chromium-1223 + headless-shell +
+  ffmpeg), root-owned, world-readable. Installed via `infra-ops`.
+- Discovery: `PLAYWRIGHT_BROWSERS_PATH=/opt/ms-playwright` set globally in
+  `/etc/environment` (PAM/all sessions) + `/etc/profile.d/playwright-browsers.sh`
+  (login shells). A project just `npm i playwright` (skip-browser-download is fine) and
+  resolves the shared binary; verified launching headless from `/opt` as a normal user.
+- To add more browsers / bump: `ssh infra-ops@10.100.10.50 'sudo env
+  PLAYWRIGHT_BROWSERS_PATH=/opt/ms-playwright npx -y playwright install <browser>'`.
 
 ## Notes