chore: gitignore .hermes/ working directory; drop tracked plan artifact

The 4533-line dashboard-OAuth plan was checked into .hermes/plans/
during initial development. .hermes/ is the Hermes Agent's runtime
working directory (logs, session caches, in-flight plans) — its
contents are never artifacts of the codebase and should not have been
tracked.

Add .hermes/ to .gitignore so future agent runs that materialise
plans/audits/cache files in the working tree don't accidentally stage
them. Remove the existing plan file from version control.

The plan content is preserved in the branch history if anyone needs to
reference it.

.gitignore

@@ -81,4 +81,8 @@ website/static/api/skills-index.json
 models-dev-upstream/
 hermes_cli/tui_dist/*
 hermes_cli/scripts/
-docs/superpowers/*
+docs/superpowers/*
+# Working directory for the Hermes Agent's session state (~/.hermes/ at runtime;
+# also created in-repo when an agent operates in this checkout). Plans, audit
+# logs, and per-session caches are never artifacts of the codebase.
+.hermes/