Browser tools find agent-browser only in PM's store or on PATH and their
readiness check never installs it, so a fresh install silently had no
browser_* tools. Package.default marks an optional package that a bare
`pm install` also carries; a failed download of it warns instead of
failing the install. `pm install --without NAME` records the opt-out in
declined-packages.json beside PM's install state, and naming the package
explicitly clears it. agent-browser and chromium gain a Termux gap: Termux
owns its browser stack and there is no bionic Chromium.
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