feat: add thinking-process artifact component

[juliarvalenti]

Summary

• Adds the thinking-process artifact component for visualizing AI reasoning, decision-making steps, and workflow progress
• Based on contribution from @jaswantsingh09 in PR component: thinking process artifact #5, with pattern fixes applied

Fixes Applied

• types.ts: Named zod import ({ z }), exported ReasoningStepZod/StepMetricZod/ProcessStepStatusZod with .describe() annotations; removed unnecessary ArtifactTabZod discriminated union; added ReasoningStep/StepMetric type exports
• action.ts: Added Zod validation for stepsJson/metricsJson parsing; use direct ThinkingProcessArtifact["data"] type instead of Extract<ArtifactTab, ...>; removed unnecessary try/catch
• index.ts: Added missing THINKING_PROCESS_DESCRIPTION, ReasoningStepZod, StepMetricZod exports
• Registry: Added entries to artifacts.ts and artifacts.json

Files

hax/artifacts/thinking-process/
├── thinking-process.tsx   # Card with collapsible agent reasoning, step indicators, metrics
├── types.ts               # Zod schemas with .describe() annotations
├── action.ts              # CopilotKit hook with Zod validation
├── description.ts         # AI prompt guidance
├── index.ts               # Barrel exports
└── README.md              # Documentation

Test plan

• hax add artifact thinking-process installs correctly
• Component renders with sample step data (completed/in-progress/pending/error)
• CopilotKit action create_thinking_process works with AI agents
• Collapsible reasoning section toggles correctly