docs: Add DOScan architecture, changelog, and features documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: JOY

docs/CHANGELOG.md

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+# DOScan Changelog
+
+All notable changes to DOScan (DOS Chain Block Explorer) are documented in this file.
+
+---
+
+## [2026-02-01] - Testnet Feature Expansion
+
+### Added
+
+#### Frontend Features
+- **User Operations Page** (`/ops`) - ERC-4337 Account Abstraction support
+  - Integrated with `user-ops-indexer` microservice
+  - API endpoint: `https://test-ops.doscan.io`
+
+- **Homepage Stats Widget** - Display key blockchain metrics on homepage
+  - `total_blocks`, `average_block_time`, `total_txs`, `wallet_addresses`, `gas_tracker`
+
+- **Get Gas Button** - Link to DOS Faucet for testnet tokens
+  - URL: `https://faucet.doschain.com?address={address}`
+
+#### Backend Features
+- **Account Abstraction Microservice** - Backend support for ERC-4337
+  - `MICROSERVICE_ACCOUNT_ABSTRACTION_ENABLED=true`
+  - URL: `http://host.docker.internal:8090/`
+
+- **Admin Panel** - Backend administration interface
+  - `ADMIN_PANEL_ENABLED=true`
+
+- **GraphQL API** - GraphQL endpoint for queries
+  - `API_GRAPHQL_ENABLED=true`
+
+- **Sourcify Integration** - Alternative contract verification
+  - `SOURCIFY_INTEGRATION_ENABLED=true`
+  - Server: `https://sourcify.dev/server`
+
+#### Infrastructure
+- **test-stats.doscan.io** - Dedicated stats API for testnet
+  - Port: 8052
+  - Container: `test-stats`
+  - Database: testnet blockscout DB (port 7432)
+
+- **test-ops.doscan.io** - User Ops API endpoint
+  - Port: 8090
+  - Container: `user-ops-indexer`
+
+### Changed
+- Updated `NEXT_PUBLIC_STATS_API_HOST` from `stats-beta.doscan.io` to `test-stats.doscan.io`
+- Added `ops` route to nginx frontend regex for proper routing
+
+### Fixed
+- Fixed User Ops page 404 error by adding route to nginx config
+- Fixed frontend env syntax error for `NEXT_PUBLIC_HOMEPAGE_STATS`
+
+---
+
+## [2026-01-31] - User Ops Indexer Deployment
+
+### Added
+- Deployed `user-ops-indexer` container for ERC-4337 support
+- Created nginx config for `test-ops.doscan.io`
+- Added CORS headers for cross-origin API access
+
+### Configuration
+```yaml
+USER_OPS_INDEXER__INDEXER__RPC_URL: http://10.0.0.4:9650/ext/bc/.../rpc
+USER_OPS_INDEXER__INDEXER__ENTRYPOINTS__V08: "true"
+USER_OPS_INDEXER__INDEXER__ENTRYPOINTS__V08_ENTRY_POINT: "0x433709009B8330FDa32311DF1C2AFA402eD8D009"
+USER_OPS_INDEXER__DATABASE__CONNECT__URL: postgresql://postgres:@host.docker.internal:7432/blockscout
+```
+
+---
+
+## [2026-01-30] - Testnet Explorer Launch
+
+### Added
+- Full Blockscout deployment for DOS Chain Testnet
+- Frontend v2.6.0 (latest)
+- Backend v9.0.2
+
+### Services Deployed
+- Frontend (`ghcr.io/blockscout/frontend:latest`)
+- Backend (`blockscout/blockscout:latest`)
+- PostgreSQL 15
+- Redis
+- Smart Contract Verifier
+- Visualizer (Sol2UML)
+- Sig Provider
+
+### Domains Configured
+- `test.doscan.io` - Main explorer
+- `test-api.doscan.io` - API endpoint
+- `viz-beta.doscan.io` - Visualizer
+- `stats-beta.doscan.io` - Stats (legacy)
+
+---
+
+## [2026-01-23] - Initial Setup
+
+### Added
+- Initial DOScan project structure
+- Docker Compose configuration for testnet
+- Environment variable templates
+
+### Network Configuration
+- Chain ID: 3939
+- RPC: `https://test.doschain.com`
+- Blockchain ID: `e4PHth8utBAPorg4sFRTaWmDfUWf9X8nAECczGx1BJVmYBv3A`
+
+---
+
+## Pending / Roadmap
+
+### Mainnet Deployment
+- [ ] Deploy to mainnet (Chain ID: 7979)
+- [ ] Configure `doscan.io` domain
+- [ ] Set up production database
+
+### Features to Enable
+- [ ] Validators List (requires custom implementation for Avalanche L1)
+- [ ] My Account full integration with Auth0
+- [ ] Export to CSV feature
+- [ ] Public tag submission
+
+### Infrastructure
+- [ ] Set up monitoring (Prometheus/Grafana)
+- [ ] Configure automated backups
+- [ ] Set up CI/CD pipeline
+
+---
+
+## Version History
+
+| Date | Frontend | Backend | Notes |
+|------|----------|---------|-------|
+| 2026-02-01 | latest | latest | Feature expansion |
+| 2026-01-30 | v2.6.0 | v9.0.2 | Initial testnet launch |