docs: add mkdocs, update links, add architecture documentation

docs/content/adr/0006-http-framework.md

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+# ADR-0006: HTTP Framework
+
+## Status
+Accepted
+
+## Context
+The platform needs an HTTP framework for:
+- REST API endpoints
+- Middleware support (auth, logging, metrics)
+- Request/response handling
+- Route registration from modules
+- Integration with observability tools
+
+Options considered:
+1. **gin-gonic/gin** - Fast, feature-rich HTTP web framework
+2. **gorilla/mux** - Lightweight router
+3. **go-chi/chi** - Lightweight, idiomatic router
+4. **net/http** (standard library) - No external dependency
+
+## Decision
+Use **gin-gonic/gin** (v1.9.1+) as the HTTP framework.
+
+**Rationale:**
+- Fast performance (comparable to net/http)
+- Rich middleware ecosystem
+- Excellent for REST APIs
+- Easy route grouping (useful for modules)
+- Good OpenTelemetry integration support
+- Widely used and well-documented
+- Recommended in playbook-golang.md
+
+## Consequences
+
+### Positive
+- High performance
+- Easy middleware chaining
+- Route grouping supports module architecture
+- Good ecosystem support
+
+### Negative
+- Additional dependency (though lightweight)
+- Slight learning curve for developers unfamiliar with Gin
+
+### Implementation Notes
+- Install: `go get github.com/gin-gonic/gin@v1.9.1`
+- Create router in `internal/server/server.go`
+- Use route groups for module isolation: `r.Group("/api/v1/blog")`
+- Add middleware stack: logging, recovery, metrics, auth (later)
+- Support graceful shutdown via fx lifecycle
+