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-plan/phases/03-conflict-resolution.md

@@ -70,7 +70,7 @@ Task(subagent_type="cli-execution-agent", run_in_background=false, prompt=`
   ## Analysis Steps
 
   ### 0. Load Output Schema (MANDATORY)
-  Execute: cat ~/.ccw/workflows/cli-templates/schemas/conflict-resolution-schema.json
+  Execute: ccw tool exec json_builder '{"cmd":"info","schema":"conflict"}' (get schema summary)
 
   ### 1. Load Context
   - Read existing files from conflict_detection.existing_files
@@ -119,7 +119,7 @@ Task(subagent_type="cli-execution-agent", run_in_background=false, prompt=`
 
   Output to conflict-resolution.json (generated in Phase 4)
 
-  **Schema Reference**: Execute cat ~/.ccw/workflows/cli-templates/schemas/conflict-resolution-schema.json to get full schema
+  **Schema Reference**: Execute ccw tool exec json_builder '{"cmd":"info","schema":"conflict"}' to get schema summary
 
   Return JSON following the schema. Key requirements:
   - Minimum 2 strategies per conflict, max 4