feat: add json_builder tool with schema-aware JSON construction and validation

Unified tool replacing manual schema reading (cat schema) across all agents
and skills. Supports 5 commands: init (skeleton), set (incremental field
setting with instant validation), validate (full structural + semantic),
merge (dedup multiple JSONs), info (compact schema summary).

Registers 24 schemas in schema-registry.ts. Updates all agent/skill/command
files to use json_builder info/init/validate instead of cat schema references.

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

.claude/skills/workflow-test-fix/phases/02-test-context-gather.md

@@ -223,7 +223,7 @@ Execute **${angle}** exploration for task planning context. Analyze codebase fro
 ## MANDATORY FIRST STEPS (Execute by Agent)
 1. Run: ccw tool exec get_modules_by_depth '{}' (project structure)
 2. Run: rg -l "{keyword_from_task}" --type ts (locate relevant files)
-3. Execute: cat ~/.ccw/workflows/cli-templates/schemas/explore-json-schema.json (get output schema reference)
+3. Execute: ccw tool exec json_builder '{"cmd":"init","schema":"explore","output":"${sessionFolder}/exploration-${angle}.json"}' (init output + get schema info)
 
 ## Exploration Strategy (${angle} focus)
 
@@ -265,7 +265,7 @@ Execute **${angle}** exploration for task planning context. Analyze codebase fro
 - _metadata.exploration_angle: "${angle}"
 
 ## Success Criteria
-- [ ] Schema obtained via cat explore-json-schema.json
+- [ ] Schema initialized via json_builder init
 - [ ] get_modules_by_depth.sh executed
 - [ ] At least 3 relevant files identified with ${angle} rationale
 - [ ] Patterns are actionable (code examples, not generic advice)