ignore the generated tool-loader extension

The platform writes extensions/tool-loader on every boot from its own source, so
it is a build artifact sitting in a repository meant to be forked. Tracking it
would hand every fork a conflict whenever the platform's copy changed.

Nothing else in here needs ignoring: a plugin's capabilities are now read from
the plugin's own directory rather than copied in, so this repository holds only
core's work and its owner's. Anything else that turns up untracked is worth
looking at rather than adding to the ignore list.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

.gitignore

@@ -0,0 +1,9 @@
+# Generated by the platform on every boot — `servers/ensure-tool-loader.ts` writes it, and it is derived
+# from source in the platform repository rather than authored here. Tracking it would mean a fork carrying
+# a build artifact and getting a conflict on it whenever the platform's copy changed.
+#
+# This is the ONLY thing in here that is not either core's or the owner's. A plugin's capabilities are read
+# from the plugin's own directory and never copied in — see platform/docs/plugin-capabilities.md — so
+# nothing else needs ignoring, and anything that turns up untracked here is worth looking at rather than
+# adding to this file.
+/extensions/