add gitignore and commit Obsidian vault config

Exclude .env (a GOOGLE_CLOUD_PROJECT value was present at the repo root),
.claude/settings.local.json, OS cruft, and personal Obsidian workspace
state (workspace.json, workspace-mobile.json, cache). Commit the rest of
.obsidian/ so the vault reopens with the same plugins, graph settings,
and daily-notes config on any machine.

Also expand Obsidian's userIgnoreFilters so .claude, .env, and .gitignore
don't pollute the file explorer, search, or graph view.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,16 @@
+# Secrets — never commit
+.env
+.env.local
+.env.*.local
+
+# OS cruft
+.DS_Store
+Thumbs.db
+
+# Claude Code — user-specific settings only; agent defs + commands stay committed
+.claude/settings.local.json
+
+# Obsidian — commit the vault config, ignore personal workspace state
+.obsidian/workspace.json
+.obsidian/workspace-mobile.json
+.obsidian/cache