refactor(doctor): redesign with 3-tier output and consolidated checks

Consolidate 16 separate checks into 5 (system, config, providers, tools, models).
Add 3-tier formatting: default (problems-only), --status (dashboard), --verbose (deep diagnostics).
Read actual loaded plugin version from opencode cache directory.
Check environment variables for provider authentication.

src/cli/doctor/format-default.ts

@@ -0,0 +1,35 @@
+import color from "picocolors"
+import type { DoctorResult } from "./types"
+import { SYMBOLS } from "./constants"
+import { formatHeader, formatIssue } from "./format-shared"
+
+export function formatDefault(result: DoctorResult): string {
+  const lines: string[] = []
+
+  lines.push(formatHeader())
+
+  const allIssues = result.results.flatMap((r) => r.issues)
+
+  if (allIssues.length === 0) {
+    const opencodeVer = result.systemInfo.opencodeVersion ?? "unknown"
+    const pluginVer = result.systemInfo.pluginVersion ?? "unknown"
+    lines.push(
+      ` ${color.green(SYMBOLS.check)} ${color.green(
+        `System OK (opencode ${opencodeVer} · oh-my-opencode ${pluginVer})`
+      )}`
+    )
+  } else {
+    const issueCount = allIssues.filter((i) => i.severity === "error").length
+    const warnCount = allIssues.filter((i) => i.severity === "warning").length
+
+    const totalStr = `${issueCount + warnCount} ${issueCount + warnCount === 1 ? "issue" : "issues"}`
+    lines.push(` ${color.yellow(SYMBOLS.warn)} ${totalStr} found:\n`)
+
+    allIssues.forEach((issue, index) => {
+      lines.push(formatIssue(issue, index + 1))
+      lines.push("")
+    })
+  }
+
+  return lines.join("\n")
+}