chore(docs): refresh agent docs, guard doc paths, archive plans (#4203)

Agent-instruction and architecture docs had drifted from the code:

- CLAUDE.md: slim to commands + pointers; fix wrong claim that
  `make pre-commit` is the full pre-PR gate (that is `make pre-pr`);
  drop stale pre-#3929 file paths and merged bug narratives
- AGENTS.md: drop dead `rust-refactor-helper` skill rule and the
  hand-maintained (already stale) scoped-AGENTS index; link
  architecture docs from Sources of Truth
- .github/AGENTS.md: replace the outdated copied CI command matrix
  with a pointer to ci.yml
- crates/AGENTS.md: merge duplicated Testing sections
- ARCHITECTURE.md: resolve the utils->config contradiction (edges are
  removed), mark volatile counts as snapshots, fix a bad path
- docs/architecture: add README router; move one-shot plans/trackers
  (rebalance-decommission phases, migration-progress ledger, PR
  template) to docs/superpowers/plans with archive headers; fix stale
  source paths in kept inventories (core/sets.rs, core/pools.rs,
  store/mod.rs, startup_* split from #3671)
- docs/operations/tier-ilm-debugging.md: extracted tier debugging
  playbook with corrected paths
- scripts/check_doc_paths.sh: new guard failing pre-commit/pre-pr when
  instruction/architecture docs reference nonexistent file paths
- .claude/skills: add tier-debug and arch-checks repo skills;
  .gitignore now keeps .claude/skills and docs/operations committable

Verification: ./scripts/check_doc_paths.sh,
./scripts/check_architecture_migration_rules.sh (both pass)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -4,7 +4,9 @@
 .vscode
 .cursor
 .direnv/
-.claude/
+# Ignore local Claude state but keep shared repo skills committable
+.claude/*
+!.claude/skills
 .tmp/
 /test
 /logs
@@ -51,6 +53,10 @@ __pycache__/
 docs/*
 !docs/architecture/
 !docs/architecture/**
+!docs/operations/
+!docs/operations/**
+!docs/superpowers/
+!docs/superpowers/**
 docs/heal-scanner-logging-governance.md
 docs/benchmark/rustfs-target-bench/
 docs/benchmark/*.md
@@ -74,3 +80,6 @@ crates/*/docs
 fuzz/target
 outputs
 worktrees/*
+
+# Local AI-agent review artifacts (omo evidence dumps)
+.omo/