docs: add roadmap and feature planning

[gimi555]

Overview

This PR adds a new Roadmap.md document containing the planned direction, feature roadmap, and improvement strategy for DebugProbe.

The goal is to provide a clearer long-term vision for the project while organizing future development into structured and realistic phases.

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Added

• New Roadmap.md documentation
• Product vision and project direction
• Current feature overview
• Planned feature roadmap
• Security and production-readiness plans
• Outgoing HTTP capture planning
• Persistence and observability planning
• UI and developer experience improvements
• Long-term distributed tracing ideas

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Roadmap Highlights

Phase 0 — Foundation & Safety

• Response header capture
• /debug authentication
• Safer defaults
• Capture size limits
• Sensitive data redaction

Phase 1 — Outgoing HTTP Capture

• HttpClient instrumentation
• Correlation tracking
• External API visibility
• Outgoing request dashboard

Phase 2 — Persistence & Storage

• Pluggable sink architecture
• File/SQLite storage
• Export/import support

Phase 3 — Metrics & Observability

• Request metrics
• Latency statistics
• Embedded charts
• Filtering and search

Phase 4+ — DX & Distributed Tracing

• UI modernization
• Replay support
• OpenTelemetry integration
• Remote trace aggregation

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Purpose

This roadmap is intended to:

• Help organize future development
• Make project direction clearer for contributors
• Prioritize production-readiness improvements
• Provide visibility into upcoming features
• Encourage community feedback and discussion

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Notes

This PR only adds documentation and does not change runtime behavior.