chore: sync Obsidian state + fix .gitignore gaps

Modified files (Obsidian saved state):
  appearance.json       — CSS snippets enabled (Obsidian confirmed)
  community-plugins.json — Excalidraw + Banners enabled (Obsidian confirmed)
  graph.json            — Obsidian reset on close (expected)
  workspace.json        — welcome.canvas added as first tab by Obsidian
  README.md             — cover GIF header preserved by Obsidian
  welcome.canvas        — user added Cosmic Brain GIF at top

.gitignore additions:
  ????-??-??.md    — daily notes from Calendar plugin (personal)
  Excalidraw/      — user Excalidraw drawings (personal, not vault content)
  Untitled.canvas  — unnamed scratch canvases
  Claude SEO*.gif/png — personal brand assets in vault root

README.md

@@ -1,6 +1,3 @@
-<p align="center">
-  <img src="cover.gif" alt="Cosmic Brain" width="100%" />
-</p>
 
 # cosmic-brain