chore: remove committed PR infographics and gitignore the path (#54564)

PR infographics are rendered locally and embedded in PR descriptions via
the image-provider (fal.media) URL — they were never meant to live in the
repo. The intended .gitignore enforcement (documented as added back in May
2026) was never actually committed, so 35 PNGs (~54MB) accumulated under
infographic/ via 'docs: add PR infographic for X' commits.

- Remove all 35 tracked infographic/*.png files.
- Add infographic/ to .gitignore so git add on the path is now a no-op.

The PR body remains the archive for these images.

.gitignore

@@ -137,3 +137,9 @@ RELEASE_v*.md
 # Desktop demo-run scratch output (hermes writes demo/*.txt during recorded
 # walkthroughs). Throwaway artifacts, never part of the app.
 apps/desktop/demo/
+
+# PR infographics are rendered locally and embedded in PR descriptions via the
+# image-provider (fal.media) URL — they are NEVER committed to the repo. The
+# PR body is the archive. See the hermes-agent-dev skill's
+# pr-infographic-workflow reference (storage rule + lapse #8 / #COMMIT-1).
+infographic/