docs: add mkdocs, update links, add architecture documentation

docs/content/adr/0008-error-handling-strategy.md

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+# ADR-0008: Error Handling Strategy
+
+## Status
+Accepted
+
+## Context
+Go's error handling philosophy requires explicit error checking. We need a consistent approach for:
+- Error creation and wrapping
+- Error propagation
+- Error classification (domain vs infrastructure)
+- Error reporting (logging, monitoring)
+- HTTP error responses
+
+## Decision
+Adopt a **wrapped error pattern** with **structured error types**:
+
+1. **Error Wrapping**: Use `fmt.Errorf("context: %w", err)` for error wrapping
+2. **Error Types**: Define custom error types for domain errors
+3. **Error Classification**: Distinguish between:
+   - Domain errors (business logic failures)
+   - Infrastructure errors (external system failures)
+   - Validation errors (input validation failures)
+4. **Error Context**: Always wrap errors with context about where they occurred
+
+**Rationale:**
+- Follows Go 1.13+ error wrapping best practices
+- Enables error inspection with `errors.Is()` and `errors.As()`
+- Maintains error chains for debugging
+- Allows structured error handling
+
+## Consequences
+
+### Positive
+- Full error traceability through call stack
+- Can inspect and handle specific error types
+- Better debugging with error context
+- Aligns with Go best practices
+
+### Negative
+- Requires discipline to wrap errors consistently
+- Can be verbose in some cases
+
+### Implementation Notes
+- Always wrap errors: `return nil, fmt.Errorf("failed to load config: %w", err)`
+- Create error types for domain errors:
+  ```go
+  type ConfigError struct {
+      Key   string
+      Cause error
+  }
+  func (e *ConfigError) Error() string { ... }
+  func (e *ConfigError) Unwrap() error { return e.Cause }
+  ```
+- Use `errors.Is()` and `errors.As()` for error checking
+- Log errors with context before returning
+- Map domain errors to HTTP status codes in handlers
+