docs: document Chromium toolchain and shared-lib requirement

docs/configuration.md

@@ -243,6 +243,9 @@ When X mode is opted in, bootstrap also requires `curl` and `jq` before arming t
 `tasks-axi` and `quota-axi` are required bootstrap tools in every profile, the same class as `lavish-axi`.
 An absent or incompatible `tasks-axi` reports `MISSING: tasks-axi (install: npm install -g tasks-axi)`; when `config/backlog-backend` is not `manual` and compatible `tasks-axi` is on `PATH`, bootstrap stays silent and firstmate uses its verbs for routine backlog mutations, otherwise it hand-edits `data/backlog.md` until installation is approved and completed.
 An absent `quota-axi` reports `MISSING: quota-axi (install: npm install -g quota-axi)`; `bin/fm-dispatch-select.sh` still degrades to the first profile at runtime when quota data is unavailable.
+`chrome-devtools-axi`'s headless launches also need a real Chromium binary and its OS-level shared-library dependencies, but bootstrap does not yet detect or report this the way it does for `tasks-axi` and `quota-axi` above; no `MISSING: chromium` line exists today.
+The binary alone is not enough: on Debian/Ubuntu-family hosts a cached Playwright Chromium binary such as `~/.cache/ms-playwright/chromium-<version>/chrome-linux64/chrome` can still be missing OS-level shared libraries like `libnspr4` that are not installed by default.
+Until bootstrap gains that detection, install it yourself before session start with `npx --yes playwright install-deps chromium`.
 Bootstrap also reports a `TANGLE:` line when `FM_ROOT` is on a named non-default branch; follow the printed checkout remediation rather than treating it as an installable tool problem.
 In a read-only session that did not get the fleet lock, the same line is advisory and omits the checkout command.
 The locked session-start bootstrap step also runs a best-effort project clone refresh through `fm-fleet-sync.sh`.