feat(git): /git overview page and diff viewer

Add git module with repo status overview (/git) and per-repo detail page
(/git/[repo]) featuring a color-coded diff viewer (+ green, - red).
Reads repo paths from REPO_PATHS env var, calls ops-agent git_status and
git_diff commands. Status badges: clean (green), dirty (orange),
behind-origin (blue).

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

app/git/[repo]/_components/diff-viewer.tsx

@@ -0,0 +1,141 @@
+'use client'
+
+import { useCallback, useEffect, useState } from 'react'
+
+async function fetchDiff(repoPath: string): Promise<string> {
+  const res = await fetch('/api/agent/exec', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ command_key: 'git_diff', args: [repoPath] }),
+  })
+
+  if (!res.ok) {
+    const text = await res.text()
+    throw new Error(`agent ${res.status}: ${text}`)
+  }
+
+  const reader = res.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:')) {
+        try {
+          const parsed = JSON.parse(line.slice(5).trim()) as { data?: string }
+          if (parsed.data !== undefined) output += parsed.data
+        } catch {
+          // ignore malformed
+        }
+      }
+    }
+  }
+
+  return output
+}
+
+function DiffLine({ line }: { line: string }) {
+  if (line.startsWith('+++') || line.startsWith('---')) {
+    return <span className="text-muted-foreground">{line}{'\n'}</span>
+  }
+  if (line.startsWith('+')) {
+    return (
+      <span className="bg-green-500/10 text-green-700 dark:text-green-400 block">
+        {line}{'\n'}
+      </span>
+    )
+  }
+  if (line.startsWith('-')) {
+    return (
+      <span className="bg-red-500/10 text-red-700 dark:text-red-400 block">
+        {line}{'\n'}
+      </span>
+    )
+  }
+  if (line.startsWith('@@')) {
+    return <span className="text-blue-600 dark:text-blue-400">{line}{'\n'}</span>
+  }
+  if (line.startsWith('diff ') || line.startsWith('index ')) {
+    return <span className="text-muted-foreground font-semibold">{line}{'\n'}</span>
+  }
+  return <span>{line}{'\n'}</span>
+}
+
+type Props = {
+  repoPath: string
+  initialDiff: string
+  initialError: string | null
+}
+
+export default function DiffViewer({ repoPath, initialDiff, initialError }: Props) {
+  const [diff, setDiff] = useState(initialDiff)
+  const [error, setError] = useState(initialError)
+  const [refreshing, setRefreshing] = useState(false)
+
+  const refresh = useCallback(async () => {
+    setRefreshing(true)
+    try {
+      const data = await fetchDiff(repoPath)
+      setDiff(data)
+      setError(null)
+    } catch (err) {
+      setError(err instanceof Error ? err.message : 'failed')
+    } finally {
+      setRefreshing(false)
+    }
+  }, [repoPath])
+
+  useEffect(() => {
+    const id = setInterval(refresh, 30000)
+    return () => clearInterval(id)
+  }, [refresh])
+
+  if (error) {
+    return (
+      <div className="rounded-lg border border-destructive/30 bg-destructive/10 px-4 py-3 text-sm text-destructive">
+        {error}
+      </div>
+    )
+  }
+
+  return (
+    <div className="space-y-2">
+      <div className="flex items-center justify-between">
+        <span className="text-xs text-muted-foreground">git diff HEAD</span>
+        <div className="flex items-center gap-2">
+          {refreshing && (
+            <span className="text-xs text-muted-foreground animate-pulse">refreshing…</span>
+          )}
+          <button
+            onClick={refresh}
+            disabled={refreshing}
+            className="text-xs text-muted-foreground hover:text-foreground transition-colors"
+          >
+            Refresh
+          </button>
+        </div>
+      </div>
+      {diff.trim() === '' ? (
+        <div className="rounded-lg border border-border px-4 py-8 text-center text-sm text-muted-foreground">
+          No uncommitted changes
+        </div>
+      ) : (
+        <pre className="overflow-x-auto rounded-lg border border-border bg-muted/30 p-4 text-xs font-mono leading-relaxed">
+          {diff.split('\n').map((line, i) => (
+            <DiffLine key={i} line={line} />
+          ))}
+        </pre>
+      )}
+    </div>
+  )
+}