Root `npm install` no longer installs agent-browser (it's not a root
package.json dependency anymore, see #43564) -- update docs that told
users to run it for that purpose, or that credited it with installing
"browser tools".
- browser.md: agent-browser resolves automatically via npx; a global
npm install -g is now presented as an optional way to skip the
one-time npx fetch, not a required step.
- browser-provider-plugin.md: fix stale comment claiming post_setup
"agent_browser" installs the npm dep -- it only ensures Chromium now.
- CONTRIBUTING.md: relabel the two optional `npm install` steps as
docs-site/workspace dependencies rather than "browser tools".
- termux.md: drop the now-pointless `npm install` from the manual
Node-dependencies step; Node.js itself is the only prerequisite,
agent-browser resolves lazily via npx same as everywhere else.
44170c2713