📝 docs(restructure): split AGENTS.md into focused guides (Tâche 6 Phase B)

Création de 9 fichiers neufs pour décharger AGENTS.md (1296 lignes →
~130) en documents lazy-loadables, compatibles avec la limite de
contexte 128k de Mistral Vibe (cf. ARCODANGE migration Phase 1,
Tâche 6 du curriculum).

Sept guides ciblés sous documentation/ :
- HISTORY.md            : phases historiques 1-9 du développement
- CLI.md                : commandes CLI, server lifecycle, config DLC_*
- API.md                : endpoints REST, OpenAPI, Greet v1/v2
- OBSERVABILITY.md      : OpenTelemetry + Jaeger, sampler types, test
- TROUBLESHOOTING.md    : issues connues + pointeurs vers guides spé
- CODE_EXAMPLES.md      : snippets endpoint/logging/context, pointeurs ADR
- ROADMAP.md            : potential features, architectural improvements

Deux fichiers racine :
- CHANGELOG.md          : user-facing, format Keep a Changelog
- AGENT_CHANGELOG.md    : décisions structurantes des agents AI
                          (référencé par AGENTS.md, n'existait pas)

Le contenu est extrait fidèlement d'AGENTS.md sans réinterprétation.
Phase C (réécriture AGENTS.md court) suit dans le commit suivant.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

documentation/ROADMAP.md

@@ -0,0 +1,40 @@
+# Roadmap & Future Enhancements
+
+Tracking pending features and architectural improvements. Extracted from the original `AGENTS.md` (Tâche 6 restructure). Status updated continuously — items move to "Completed Features" section once shipped.
+
+## Potential Features
+
+- [ ] Database integration
+- [ ] Authentication / Authorization
+- [ ] Rate limiting
+- [ ] Metrics and monitoring
+- [ ] Docker containerization
+- ✅ CI/CD pipeline ([ADR-0016](../adr/0016-ci-cd-pipeline-design.md), [ADR-0017](../adr/0017-trunk-based-development-workflow.md))
+- [ ] Configuration hot reload
+- [ ] Circuit breakers
+
+## Architectural Improvements
+
+- [ ] Request validation middleware
+- ✅ OpenAPI / Swagger documentation with embedded spec
+- [ ] Enhanced OpenTelemetry instrumentation
+- [ ] Metrics collection and visualization
+- [ ] Health check improvements
+- [ ] Configuration validation enhancements
+
+## Completed Features
+
+- ✅ Graceful shutdown with readiness endpoint
+- ✅ OpenTelemetry integration with Jaeger support
+- ✅ Configuration management with Viper
+- ✅ Comprehensive logging with Zerolog
+- ✅ Build system with binary output
+- ✅ Complete documentation with commit conventions
+- ✅ Version management with runtime info
+
+## How to Propose a New Feature
+
+1. Open a Gitea issue describing the use case and acceptance criteria
+2. If the feature implies an architectural decision, draft an ADR (`adr/<NNNN>-<slug>.md`) following the template
+3. Reference the ADR + issue in any PR introducing the feature
+4. Update this roadmap (move from "Potential" to "Completed" when shipped)