Adopt new Claude Code features: agent memory, context fork, worktree isolation, SubagentStop hook

- Add `memory: project` to 14 specialist agents for cross-session learning
- Add `context: fork` + `agent:` to 6 analysis skills to preserve main context
- Add `isolation: worktree` to prototyper agent for safe throwaway experiments
- Add SubagentStop hook to complete agent audit trail (start + stop logging)

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

.claude/skills/asset-audit/SKILL.md

@@ -4,6 +4,8 @@ description: "Audits game assets for compliance with naming conventions, file si
 argument-hint: "[category|all]"
 user-invocable: true
 allowed-tools: Read, Glob, Grep
+context: fork
+agent: Explore
 ---
 
 When this skill is invoked:

.claude/skills/balance-check/SKILL.md

@@ -4,6 +4,8 @@ description: "Analyzes game balance data files, formulas, and configuration to i
 argument-hint: "[system-name|path-to-data-file]"
 user-invocable: true
 allowed-tools: Read, Glob, Grep
+context: fork
+agent: Explore
 ---
 
 When this skill is invoked:

.claude/skills/code-review/SKILL.md

@@ -4,6 +4,8 @@ description: "Performs an architectural and quality code review on a specified f
 argument-hint: "[path-to-file-or-directory]"
 user-invocable: true
 allowed-tools: Read, Glob, Grep, Bash
+context: fork
+agent: code-reviewer
 ---
 
 When this skill is invoked:

.claude/skills/design-review/SKILL.md

@@ -4,6 +4,8 @@ description: "Reviews a game design document for completeness, internal consiste
 argument-hint: "[path-to-design-doc]"
 user-invocable: true
 allowed-tools: Read, Glob, Grep
+context: fork
+agent: Explore
 ---
 
 When this skill is invoked:

.claude/skills/project-stage-detect/SKILL.md

@@ -4,6 +4,8 @@ description: "Automatically analyze project state, detect stage, identify gaps,
 argument-hint: "[optional: role filter like 'programmer' or 'designer']"
 user-invocable: true
 allowed-tools: Read, Glob, Grep, Bash
+context: fork
+agent: Explore
 ---
 
 # Project Stage Detection

.claude/skills/reverse-document/SKILL.md

@@ -4,6 +4,8 @@ description: "Generate design or architecture documents from existing implementa
 argument-hint: "<type> <path> (e.g., 'design src/gameplay/combat' or 'architecture src/core')"
 user-invocable: true
 allowed-tools: Read, Glob, Grep, Write, Edit, Bash
+context: fork
+agent: Explore
 ---
 
 # Reverse Documentation