Initial commit: E4B-MarkBase model integration with passing tests

- E4B-MarkBase model (42 layers, 4.4GB) loaded successfully
- All Phase 1-6 tests passed (model loading, forward pass, vision/audio towers, token generation, performance)
- All stress tests passed (5/5 in 127.6s)
  - Concurrent inference
  - Memory stress (67.5 tok/s, 0 NaN)
  - Continuous generation
  - Batch processing
  - Long-running stability
- Swift Metal inference engine with multimodal support

Sources/MarkBaseServer/PerformanceMetrics.swift

@@ -0,0 +1,152 @@
+import Foundation
+
+// ─────────────────────────────────────────────────────────────
+// Performance Metrics API Models
+// Prometheus Compatible Format
+// ─────────────────────────────────────────────────────────────
+
+/// Performance metrics collector
+public final class MetricsCollector {
+    public nonisolated(unsafe) static let shared = MetricsCollector()
+    
+    private var counters: [String: CounterMetric] = [:]
+    private var histograms: [String: MutableHistogram] = [:]
+    private let lock = NSLock()
+    
+    private init() {}
+    
+    /// Record a request
+    public func recordRequest(duration: TimeInterval, tokens: Int, model: String) {
+        lock.lock()
+        defer { lock.unlock() }
+        
+        // Request count
+        incrementCounter(name: "markbase_requests_total", labels: ["model": model])
+        
+        // Request duration
+        observeHistogram(name: "markbase_request_duration_seconds", value: duration, labels: ["model": model])
+        
+        // Tokens processed
+        incrementCounter(name: "markbase_tokens_total", labels: ["model": model, "type": "output"], value: Double(tokens))
+    }
+    
+    /// Record a token generation
+    public func recordToken(tokens: Int, duration: TimeInterval, model: String) {
+        lock.lock()
+        defer { lock.unlock() }
+        
+        let tokensPerSecond = Double(tokens) / duration
+        observeHistogram(name: "markbase_tokens_per_second", value: tokensPerSecond, labels: ["model": model])
+    }
+    
+    /// Record an error
+    public func recordError(type: String, model: String) {
+        lock.lock()
+        defer { lock.unlock() }
+        
+        incrementCounter(name: "markbase_errors_total", labels: ["model": model, "type": type])
+    }
+    
+    /// Get Prometheus format metrics
+    public func getPrometheusMetrics() -> String {
+        lock.lock()
+        defer { lock.unlock() }
+        
+        var output = ""
+        
+        for (name, counter) in counters {
+            output += counter.toPrometheus(name: name)
+        }
+        
+        for (name, histogram) in histograms {
+            output += histogram.toPrometheus(name: name)
+        }
+        
+        return output
+    }
+    
+    // ─────────────────────────────────────────────────────────────
+    // Private helpers
+    // ─────────────────────────────────────────────────────────────
+    
+    private func incrementCounter(name: String, labels: [String: String], value: Double = 1.0) {
+        if counters[name] == nil {
+            counters[name] = CounterMetric()
+        }
+        counters[name]?.increment(by: value, labels: labels)
+    }
+    
+    private func observeHistogram(name: String, value: Double, labels: [String: String]) {
+        if histograms[name] == nil {
+            histograms[name] = MutableHistogram()
+        }
+        histograms[name]?.observe(value, labels: labels)
+    }
+}
+
+// ─────────────────────────────────────────────────────────────
+// Metric types
+// ─────────────────────────────────────────────────────────────
+
+protocol Metric {
+    func toPrometheus(name: String) -> String
+}
+
+struct CounterMetric: Metric {
+    var values: [[String: String]: Double] = [:]
+    
+    mutating func increment(by value: Double, labels: [String: String]) {
+        values[labels, default: 0] += value
+    }
+    
+    func toPrometheus(name: String) -> String {
+        var output = "# TYPE \(name) counter\n"
+        
+        for (labels, value) in values {
+            let labelsStr = labels.map { "\($0.key)=\"\($0.value)\"" }.joined(separator: ",")
+            output += "\(name){\(labelsStr)} \(value)\n"
+        }
+        
+        return output + "\n"
+    }
+}
+
+struct HistogramMetric: Metric {
+    var counts: [[String: String]: Int] = [:]
+    var sums: [[String: String]: Double] = [:]
+    
+    mutating func observe(_ value: Double, labels: [String: String]) {
+        counts[labels, default: 0] += 1
+        sums[labels, default: 0] += value
+    }
+    
+    func toPrometheus(name: String) -> String {
+        var output = "# TYPE \(name) histogram\n"
+        
+        for (labels, count) in counts {
+            let sum = sums[labels] ?? 0
+            let labelsStr = labels.map { "\($0.key)=\"\($0.value)\"" }.joined(separator: ",")
+            output += "\(name)_count{\(labelsStr)} \(count)\n"
+            output += "\(name)_sum{\(labelsStr)} \(sum)\n"
+        }
+        
+        return output + "\n"
+    }
+}
+
+// Wrapper for mutable histogram
+final class MutableHistogram {
+    var histogram: HistogramMetric
+    
+    init() {
+        self.histogram = HistogramMetric()
+    }
+    
+    func observe(_ value: Double, labels: [String: String]) {
+        histogram.observe(value, labels: labels)
+    }
+    
+    func toPrometheus(name: String) -> String {
+        histogram.toPrometheus(name: name)
+    }
+}