feat(docker): agent-client helper, Docker container list page

- lib/agent-client.ts: server-side execAgent() that calls the ops-agent
  directly via OPS_AGENT_URL/OPS_AGENT_SECRET and streams SSE output
- lib/parse-docker.ts: pure parser for fixed-width docker ps table output
- app/docker/page.tsx: server component that fetches initial container list
  and passes it to the client component
- app/docker/_components/docker-table.tsx: client component with 5s
  auto-refresh via useEffect, status badge, and Link to /docker/[name]
- app/docker/[name]/page.tsx: placeholder detail page (logs in Story 3)

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

lib/agent-client.ts

@@ -0,0 +1,58 @@
+import 'server-only'
+
+const AGENT_URL = process.env.OPS_AGENT_URL ?? 'http://127.0.0.1:3099'
+const AGENT_SECRET = process.env.OPS_AGENT_SECRET ?? ''
+
+export async function execAgent(
+  commandKey: string,
+  args: string[] = [],
+  onChunk?: (chunk: string) => void,
+): Promise<string> {
+  const response = await fetch(`${AGENT_URL}/agent/v1/exec`, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      Authorization: `Bearer ${AGENT_SECRET}`,
+    },
+    body: JSON.stringify({ command_key: commandKey, args }),
+    cache: 'no-store',
+  })
+
+  if (!response.ok) {
+    const text = await response.text()
+    throw new Error(`agent error ${response.status}: ${text}`)
+  }
+
+  const reader = response.body?.getReader()
+  if (!reader) throw new Error('no response body')
+
+  const decoder = new TextDecoder()
+  let buffer = ''
+  let output = ''
+
+  while (true) {
+    const { done, value } = await reader.read()
+    if (done) break
+
+    buffer += decoder.decode(value, { stream: true })
+    const lines = buffer.split('\n')
+    buffer = lines.pop() ?? ''
+
+    for (const line of lines) {
+      if (line.startsWith('data:')) {
+        const jsonStr = line.slice(5).trim()
+        try {
+          const parsed = JSON.parse(jsonStr) as { data?: string }
+          if (parsed.data !== undefined) {
+            output += parsed.data
+            onChunk?.(parsed.data)
+          }
+        } catch {
+          // skip malformed SSE data
+        }
+      }
+    }
+  }
+
+  return output
+}

lib/parse-docker.ts

@@ -0,0 +1,40 @@
+export type Container = {
+  id: string
+  image: string
+  command: string
+  created: string
+  status: string
+  ports: string
+  name: string
+}
+
+// Parse the fixed-width table output of `docker ps --format table`
+export function parseDockerPs(output: string): Container[] {
+  const lines = output.trim().split('\n').filter(Boolean)
+  if (lines.length < 2) return []
+
+  const header = lines[0]
+
+  const COLS = ['CONTAINER ID', 'IMAGE', 'COMMAND', 'CREATED', 'STATUS', 'PORTS', 'NAMES'] as const
+  const positions = COLS.map((col) => header.indexOf(col))
+
+  // Must find at least NAMES (last) to produce useful output
+  if (positions[6] === -1) return []
+
+  const extract = (line: string, i: number): string => {
+    const start = positions[i]
+    if (start === -1) return ''
+    const nextIdx = positions.slice(i + 1).find((p) => p !== -1)
+    return line.slice(start, nextIdx).trim()
+  }
+
+  return lines.slice(1).map((line) => ({
+    id: extract(line, 0),
+    image: extract(line, 1),
+    command: extract(line, 2),
+    created: extract(line, 3),
+    status: extract(line, 4),
+    ports: extract(line, 5),
+    name: extract(line, 6),
+  }))
+}