refactor(context): Extract context modules from god object

- Create src/context/docker.js - Docker operations
- Create src/context/caddy.js - Caddyfile manipulation
- Create src/context/dns.js - DNS token management and API calls
- Create src/context/session.js - Session wrapper
- Create src/context/index.js - Context assembly (DI container)

Breaks up the 50+ property ctx god object into domain-specific modules

dashcaddy-api/src/context/docker.js

@@ -0,0 +1,67 @@
+/**
+ * Docker context - Docker client and operations
+ */
+const Docker = require('dockerode');
+const { DOCKER } = require('../../constants');
+
+const docker = new Docker();
+
+/**
+ * Pull a Docker image with timeout protection
+ */
+function dockerPull(imageName, timeoutMs = DOCKER.TIMEOUT) {
+  return new Promise((resolve, reject) => {
+    const timer = setTimeout(
+      () => reject(new Error(`Docker pull timed out after ${timeoutMs / 1000}s: ${imageName}`)),
+      timeoutMs
+    );
+    docker.pull(imageName, (err, stream) => {
+      if (err) {
+        clearTimeout(timer);
+        return reject(err);
+      }
+      docker.modem.followProgress(stream, (err, output) => {
+        clearTimeout(timer);
+        if (err) return reject(err);
+        resolve(output);
+      });
+    });
+  });
+}
+
+/**
+ * Find a running Docker container by name substring
+ */
+async function findContainerByName(name, opts = { all: false }) {
+  const containers = await docker.listContainers(opts);
+  const match = containers.find(c =>
+    c.Names.some(n => n.toLowerCase().includes(name.toLowerCase()))
+  );
+  return match || null;
+}
+
+/**
+ * Get all host ports currently in use by Docker containers
+ */
+async function getUsedPorts() {
+  const containers = await docker.listContainers({ all: false });
+  const ports = new Set();
+  for (const c of containers) {
+    for (const p of (c.Ports || [])) {
+      if (p.PublicPort) ports.add(p.PublicPort);
+    }
+  }
+  return ports;
+}
+
+function createDockerContext(dockerSecurity) {
+  return {
+    client: docker,
+    pull: dockerPull,
+    findContainer: findContainerByName,
+    getUsedPorts,
+    security: dockerSecurity,
+  };
+}
+
+module.exports = { createDockerContext };