chore(gitignore): scope gradle-facts ignores to a nested .gitignore

Move the gradle-facts-related transient patterns from the root
.gitignore into a nested .gitignore at
test/fixtures/commands/manifest/gradle-facts/. Patterns become
unanchored (`.gradle/`, `build/`, `.socket.facts.json`) and tighten
to the three things `socket manifest gradle --facts` runs actually
produce — the previously listed `pom.xml` and `local.properties`
patterns weren't generated by the --facts flow and have been dropped.

Keeps the root .gitignore tidy and makes the transience signal
visible to anyone working in the fixtures directory.

Author: jfblaa

.gitignore

@@ -21,13 +21,6 @@ Thumbs.db
 test/fixtures/commands/fix/e2e-test-js-temp-*
 test/fixtures/commands/fix/e2e-test-py-temp-*
 
-# Generated by `socket manifest gradle --facts` integration runs.
-test/fixtures/commands/manifest/gradle-facts/**/.gradle/
-test/fixtures/commands/manifest/gradle-facts/**/build/
-test/fixtures/commands/manifest/gradle-facts/**/.socket.facts.json
-test/fixtures/commands/manifest/gradle-facts/**/pom.xml
-test/fixtures/commands/manifest/gradle-facts/**/local.properties
-
 /.claude/*
 !/.claude/agents/
 !/.claude/commands/

test/fixtures/commands/manifest/gradle-facts/.gitignore

@@ -0,0 +1,5 @@
+# Generated by `socket manifest gradle --facts` runs against any of the
+# fixtures in this directory.
+.gradle/
+build/
+.socket.facts.json