Migrate to per-agent subdirectories, uniform 8-agent support, cross-platform fixes

- All paths use ~/.elydora/{agentId}/ per-agent isolation
- Add copilot, letta plugins; split kiro into kirocli + kiroide
- Remove augment (SDK-only agent, not one-click)
- Fix chmod to skip on Windows (platform check)
- Fix uninstall to filter by specific agentId
- Uniform 8 agents: claudecode, cursor, gemini, kirocli, kiroide, opencode, copilot, letta
- Update README agent table

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

src/plugins/registry.ts

@@ -8,7 +8,9 @@ export const SUPPORTED_AGENTS: ReadonlyMap<string, AgentRegistryEntry> = new Map
   ['claudecode', { name: 'Claude Code', configDir: '~/.claude', configFile: 'settings.json' }],
   ['cursor', { name: 'Cursor', configDir: '.cursor', configFile: 'hooks.json' }],
   ['gemini', { name: 'Gemini CLI', configDir: '~/.gemini', configFile: 'settings.json' }],
-  ['augment', { name: 'Augment Code', configDir: '~/.augment', configFile: 'settings.json' }],
-  ['kiro', { name: 'Kiro', configDir: '.kiro/hooks', configFile: 'elydora-audit.kiro.hook' }],
-  ['opencode', { name: 'OpenCode', configDir: '.opencode/plugins', configFile: 'elydora-audit.js' }],
+  ['kirocli', { name: 'Kiro CLI', configDir: '~/.kiro', configFile: 'settings.json' }],
+  ['kiroide', { name: 'Kiro IDE', configDir: '.kiro/hooks', configFile: 'elydora-audit.kiro.hook' }],
+  ['opencode', { name: 'OpenCode', configDir: '.config/opencode/plugins', configFile: 'elydora-audit.mjs' }],
+  ['copilot', { name: 'Copilot CLI', configDir: '.github/hooks', configFile: 'hooks.json' }],
+  ['letta', { name: 'Letta Code', configDir: '~/.letta', configFile: 'settings.json' }],
 ]);