feat: Add semver-compatible service discovery with privacy

## Breaking Changes

### Removed Endpoints
- Removed GET /users/:username/services (service listing)
- Services are now completely hidden - cannot be enumerated

### Updated Endpoints
- GET /users/:username/services/:fqn now supports semver matching
- Requesting chat@1.0.0 will match chat@1.2.3, chat@1.5.0, etc.
- Will NOT match chat@2.0.0 (different major version)

## New Features

### Semantic Versioning Support
- Compatible version matching following semver rules (^1.0.0)
- Major version must match exactly
- For major version 0, minor must also match (0.x.y is unstable)
- Available version must be >= requested version
- Prerelease versions require exact match

### Privacy Improvements
- All services are now hidden by default
- No way to enumerate or list services for a username
- Must know exact service name to discover

## Implementation

### Server (src/)
- crypto.ts: Added parseVersion(), isVersionCompatible(), parseServiceFqn()
- storage/types.ts: Added findServicesByName() interface method
- storage/sqlite.ts: Implemented findServicesByName() with LIKE query
- storage/d1.ts: Implemented findServicesByName() with LIKE query
- app.ts: Updated GET /:username/services/:fqn with semver matching

### Semver Matching Logic
- Parse requested version: chat@1.0.0 → {name: "chat", version: "1.0.0"}
- Find all services with matching name: chat@*
- Filter to compatible versions using semver rules
- Return first match (most recently created)

## Examples

Request: chat@1.0.0
Matches: chat@1.0.0, chat@1.2.3, chat@1.9.5
Does NOT match: chat@0.9.0, chat@2.0.0, chat@1.0.0-beta

🤖 Generated with Claude Code

src/storage/d1.ts

@@ -544,6 +544,20 @@ export class D1Storage implements Storage {
     return result ? (result as any).uuid : null;
   }
 
+  async findServicesByName(username: string, serviceName: string): Promise<Service[]> {
+    const result = await this.db.prepare(`
+      SELECT * FROM services
+      WHERE username = ? AND service_fqn LIKE ? AND expires_at > ?
+      ORDER BY created_at DESC
+    `).bind(username, `${serviceName}@%`, Date.now()).all();
+
+    if (!result.results) {
+      return [];
+    }
+
+    return result.results.map(row => this.rowToService(row as any));
+  }
+
   async deleteService(serviceId: string, username: string): Promise<boolean> {
     const result = await this.db.prepare(`
       DELETE FROM services