feat: Add sprint documents for feature-bench testing

- Added uninstaller feature sprint (Issue #3900)
- Added maxSteps feature sprint (Issue #3631)
- These sprints will be used by feature-bench test suite

sprints/uninstaller/opencode-01-uninstaller.md

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+# Sprint: OpenCode Uninstaller Feature
+
+## Problem Statement
+Users need a reliable way to completely remove OpenCode from their system, including all configuration files, cached data, and installed components, as outlined in [Issue #3900](https://github.com/sst/opencode/issues/3900).
+
+## Context
+### Existing System
+OpenCode is a CLI tool that installs various components and configurations across the system. Currently, there is no comprehensive uninstall command that cleanly removes all traces of the installation.
+
+### Uninstaller Feature Requirements
+The uninstaller must provide a complete removal process that:
+- Removes the OpenCode binary/executable
+- Cleans up configuration files from user directories
+- Removes cached data and temporary files
+- Provides options for selective removal (keep configs, etc.)
+- Confirms actions before destructive operations
+
+## Success Criteria
+- [ ] Uninstall command (`opencode uninstall`) is available in the CLI
+- [ ] Command removes OpenCode executable from installation path
+- [ ] Configuration files in ~/.opencode are removed (with --all flag)
+- [ ] Cache directories are cleaned up
+- [ ] User is prompted for confirmation before removal
+- [ ] Option to keep configuration files (--keep-config)
+- [ ] Uninstaller provides clear feedback on what was removed
+- [ ] Process is reversible by reinstalling OpenCode
+- [ ] Exit code 0 on successful uninstallation
+- [ ] Comprehensive error handling for permission issues
+- [ ] Documentation updated with uninstall instructions
+
+## Technical Requirements
+
+### CLI Interface
+```bash
+opencode uninstall [options]
+  --all           Remove everything including configs
+  --keep-config   Keep configuration files
+  --force         Skip confirmation prompts
+  --dry-run       Show what would be removed without doing it
+```
+
+### File Locations to Handle
+- **Binary**: `/usr/local/bin/opencode` or installation path
+- **Config**: `~/.opencode/` directory
+- **Cache**: `~/.cache/opencode/` directory
+- **Temp**: `/tmp/opencode-*` files
+- **Logs**: `~/.opencode/logs/` directory
+
+### Implementation Steps
+1. Parse command arguments and flags
+2. Identify all OpenCode-related files and directories
+3. Show user what will be removed (with confirmation)
+4. Remove files in correct order (temp -> cache -> config -> binary)
+5. Verify removal and report status
+6. Clean up any remaining symlinks or PATH entries
+
+### Error Handling
+- Permission denied errors should suggest using sudo
+- Missing files should not cause failure
+- Partial uninstall should be reported clearly
+- Network operations should have timeout handling
+
+## Testing Strategy
+1. Install OpenCode in a test container
+2. Create configuration and cache files
+3. Run uninstall command with various flags
+4. Verify complete removal of all components
+5. Test edge cases (permissions, missing files, etc.)
+6. Validate that reinstallation works after uninstall
+
+## Validation Checklist
+- [ ] Binary file removed from system
+- [ ] Config directory removed (when using --all)
+- [ ] Cache directory cleaned up
+- [ ] No orphaned files remain
+- [ ] PATH environment cleaned if modified
+- [ ] Exit codes match expected values
+- [ ] Help text includes uninstall command
+- [ ] Man page or docs updated