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

.gitignore

@@ -37,4 +37,15 @@ node_modules/
 WIKI*.md
 PROMPT.md
 *.tmp.*
-"Obsidian vault*"
+Obsidian vault*
+Untitled.canvas
+
+# Daily notes created by Calendar plugin
+????-??-??.md
+
+# Excalidraw drawings (personal, user-specific)
+Excalidraw/
+
+# Loose brand/personal GIFs and images in vault root (not _attachments/)
+Claude SEO*.gif
+Claude SEO*.png