chore(config): fix skill contradictions, gitignore .obsidian, docs cleanup

- sprint-start: remove three-tier severity (critical/warning/suggestion),
  align with pr-review policy (every comment is actionable)
- sprint-start: resolve {team_scope_dirs} dangling placeholder
- .gitignore: add .obsidian/ directory
- DEVOPS.md: remove "pending setup" from gdlint (now enforced)
- Remove GEMINI-SCAN.md one-off scan artifact

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -59,6 +59,7 @@ Thumbs.db
 # IDE
 .idea/
 .vscode/
+.obsidian/
 *.swp
 *.swo