feat: add skills system for extensible capability packages

Implement a three-tier skill system (bundled/managed/workspace) that
extends Flynn's abilities via SKILL.md instructions injected into the
system prompt.

- SkillManifest/Skill types with requirements gating (OS, binaries, env)
- Loader: discovers skills from directories, validates manifests,
  checks system requirements, infers manifest from SKILL.md if missing
- SkillRegistry: holds skills, generates system prompt additions,
  supports override by name (workspace > managed > bundled)
- SkillInstaller: copies/removes skills in managed directory with
  upgrade support
- Config: add skills.workspace_dir, managed_dir, bundled_dir options
- Daemon: loads all skills at startup, injects available skill
  instructions into the system prompt
- Tests: 45 new tests (loader 22, registry 11, installer 12)

src/daemon/index.ts

@@ -9,6 +9,7 @@ import { GatewayServer } from '../gateway/index.js';
 import { ChannelRegistry, TelegramAdapter, WebChatAdapter } from '../channels/index.js';
 import type { InboundMessage, OutboundMessage } from '../channels/index.js';
 import { McpManager } from '../mcp/index.js';
+import { SkillRegistry, SkillInstaller, loadAllSkills } from '../skills/index.js';
 import { resolve } from 'path';
 import { homedir } from 'os';
 import { mkdirSync, readFileSync, existsSync } from 'fs';
@@ -25,6 +26,8 @@ export interface DaemonContext {
   gateway: GatewayServer;
   channelRegistry: ChannelRegistry;
   mcpManager: McpManager;
+  skillRegistry: SkillRegistry;
+  skillInstaller: SkillInstaller;
 }
 
 function loadSystemPrompt(): string {
@@ -199,11 +202,35 @@ export async function startDaemon(config: Config): Promise<DaemonContext> {
     console.log('MCP servers stopped');
   });
 
+  // Initialize skills system
+  const defaultManagedDir = resolve(homedir(), '.flynn/workspace/skills');
+  const skillRegistry = new SkillRegistry();
+  const skillInstaller = new SkillInstaller(config.skills.managed_dir ?? defaultManagedDir);
+
+  const skills = loadAllSkills({
+    bundledDir: config.skills.bundled_dir,
+    managedDir: config.skills.managed_dir ?? defaultManagedDir,
+    workspaceDir: config.skills.workspace_dir,
+  });
+
+  for (const skill of skills) {
+    skillRegistry.register(skill);
+  }
+
+  if (skills.length > 0) {
+    const available = skillRegistry.listAvailable().length;
+    console.log(`Loaded ${skills.length} skill(s) (${available} available)`);
+  }
+
   // Initialize model router
   const modelRouter = createModelRouter(config);
 
-  // Load system prompt once for reuse
-  const systemPrompt = loadSystemPrompt();
+  // Load system prompt and append skill instructions
+  let systemPrompt = loadSystemPrompt();
+  const skillAdditions = skillRegistry.getSystemPromptAdditions();
+  if (skillAdditions) {
+    systemPrompt = `${systemPrompt}\n\n# Available Skills\n\n${skillAdditions}`;
+  }
 
   // Initialize gateway WebSocket server
   const gateway = new GatewayServer({
@@ -296,6 +323,8 @@ export async function startDaemon(config: Config): Promise<DaemonContext> {
     gateway,
     channelRegistry,
     mcpManager,
+    skillRegistry,
+    skillInstaller,
   };
 }