perf(hooks): improve hook efficiency with early exits and cooldowns

Sprint 8 - Hook Efficiency Quick Wins (v5.5.0)

- Remove viz-platform SessionStart hook (zero value, just echoed "loaded")
- Add early git check to git-flow branch-check.sh (skip JSON parsing for non-git commands)
- Add early git check to git-flow commit-msg-check.sh (skip Python spawn for non-commit commands)
- Add 60-second cooldown to project-hygiene cleanup.sh (reduce find operations)

Closes #321, #322, #323, #324

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/git-flow/hooks/branch-check.sh

@@ -6,6 +6,11 @@
 # Read tool input from stdin (JSON format)
 INPUT=$(cat)
 
+# Quick check - exit immediately if not a git command
+if ! echo "$INPUT" | grep -q '"command".*git'; then
+    exit 0
+fi
+
 # Extract command from JSON input
 # The Bash tool sends {"command": "..."} format
 COMMAND=$(echo "$INPUT" | grep -o '"command"[[:space:]]*:[[:space:]]*"[^"]*"' | head -1 | sed 's/.*"command"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/')