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>

docs/DEVOPS.md

@@ -134,7 +134,7 @@ The golden file (`server/tests/golden/proof_room_tick_10.json`) is a committed s
 ```bash
 make lint               # Run all linters
 make lint-server        # clippy (deny warnings) + rustfmt --check
-make lint-client        # gdlint/gdformat (pending setup)
+make lint-client        # gdlint/gdformat
 ```
 
 ### CI (Local)