docs: add implementation plan, ADRs, and task tracking system

- Add comprehensive 8-phase implementation plan (docs/plan.md)
- Add 28 Architecture Decision Records (docs/adr/) covering all phases
- Add task tracking system with 283+ task files (docs/stories/)
- Add task generator script for automated task file creation
- Add reference playbooks and requirements documentation

This commit establishes the complete planning foundation for the Go
Platform implementation, documenting all architectural decisions and
providing detailed task breakdown for Phases 0-8.

docs/stories/phase0/0.2.3-implement-internalconfigconfiggo-using-viper.md

@@ -0,0 +1,60 @@
+# Task 0.2.3: Implement Config Loader
+
+## Metadata
+- **Task ID**: 0.2.3
+- **Title**: Implement Config Loader
+- **Phase**: 0 - Project Setup & Foundation
+- **Section**: 0.2 Configuration System
+- **Status**: Pending
+- **Priority**: High
+- **Estimated Time**: 30 minutes
+- **Dependencies**: 0.2.1, 0.2.2
+
+## Description
+Implement the Viper-based configuration loader in `internal/config/` that implements the `ConfigProvider` interface. This loader will handle hierarchical configuration loading from files and environment variables.
+
+## Requirements
+- Implement `ConfigProvider` interface using Viper
+- Load configuration in order: defaults → environment-specific → env vars
+- Support YAML configuration files
+- Support environment variable overrides
+- Provide placeholder for secret manager integration (Phase 6)
+
+## Implementation Steps
+1. Create `internal/config/config.go`:
+   - Implement `ConfigProvider` interface
+   - Wrap Viper instance
+   - Implement all interface methods
+2. Create `internal/config/loader.go`:
+   - `LoadConfig()` function
+   - Load `config/default.yaml` as baseline
+   - Merge environment-specific YAML (development/production)
+   - Apply environment variable overrides
+   - Set up automatic environment variable binding
+3. Add error handling for missing config files
+4. Add logging for configuration loading
+
+## Acceptance Criteria
+- [ ] `internal/config/config.go` implements `ConfigProvider`
+- [ ] `internal/config/loader.go` has `LoadConfig()` function
+- [ ] Configuration loads from `config/default.yaml`
+- [ ] Environment-specific configs are merged correctly
+- [ ] Environment variables override file values
+- [ ] Errors are handled gracefully
+
+## Related ADRs
+- [ADR-0004: Configuration Management](../../adr/0004-configuration-management.md)
+
+## Implementation Notes
+- Use Viper's `SetConfigName()` and `AddConfigPath()`
+- Use `MergeInConfig()` for environment-specific files
+- Use `AutomaticEnv()` for environment variable binding
+- Set environment variable prefix (e.g., `GOPLT_`)
+- Use `SetEnvKeyReplacer()` to replace dots with underscores
+
+## Testing
+```bash
+# Test config loading
+go test ./internal/config -v
+```
+