feat(hooks): add HTTP hook handler support

Add type: "http" hook support matching Claude Code's HTTP hook specification.
HTTP hooks send POST requests with JSON body, support env var interpolation
in headers via allowedEnvVars, and configurable timeout.

New files:
- execute-http-hook.ts: HTTP hook execution with env var interpolation
- dispatch-hook.ts: Unified dispatcher for command and HTTP hooks
- execute-http-hook.test.ts: 14 tests covering all HTTP hook scenarios

Modified files:
- types.ts: Added HookHttp interface, HookAction union type
- config.ts: Updated to accept HookAction in raw hook matchers
- pre-tool-use/post-tool-use/stop/user-prompt-submit/pre-compact:
  Updated all 5 executors to dispatch HTTP hooks via dispatchHook()
- plugin-loader/types.ts: Added "http" to HookEntry type union

src/hooks/claude-code-hooks/execute-http-hook.ts

@@ -0,0 +1,87 @@
+import type { HookHttp } from "./types"
+import type { CommandResult } from "../../shared/command-executor/execute-hook-command"
+
+const DEFAULT_HTTP_HOOK_TIMEOUT_S = 30
+
+export function interpolateEnvVars(
+  value: string,
+  allowedEnvVars: string[]
+): string {
+  const allowedSet = new Set(allowedEnvVars)
+
+  let result = value.replace(/\$\{(\w+)\}/g, (_match, varName: string) => {
+    if (allowedSet.has(varName)) {
+      return process.env[varName] ?? ""
+    }
+    return ""
+  })
+
+  result = result.replace(/\$(\w+)/g, (_match, varName: string) => {
+    if (allowedSet.has(varName)) {
+      return process.env[varName] ?? ""
+    }
+    return ""
+  })
+
+  return result
+}
+
+function resolveHeaders(
+  hook: HookHttp
+): Record<string, string> {
+  const headers: Record<string, string> = {
+    "Content-Type": "application/json",
+  }
+
+  if (!hook.headers) return headers
+
+  const allowedEnvVars = hook.allowedEnvVars ?? []
+  for (const [key, value] of Object.entries(hook.headers)) {
+    headers[key] = interpolateEnvVars(value, allowedEnvVars)
+  }
+
+  return headers
+}
+
+export async function executeHttpHook(
+  hook: HookHttp,
+  stdin: string
+): Promise<CommandResult> {
+  const timeoutS = hook.timeout ?? DEFAULT_HTTP_HOOK_TIMEOUT_S
+  const headers = resolveHeaders(hook)
+
+  try {
+    const response = await fetch(hook.url, {
+      method: "POST",
+      headers,
+      body: stdin,
+      signal: AbortSignal.timeout(timeoutS * 1000),
+    })
+
+    if (!response.ok) {
+      return {
+        exitCode: 1,
+        stderr: `HTTP hook returned status ${response.status}: ${response.statusText}`,
+        stdout: await response.text().catch(() => ""),
+      }
+    }
+
+    const body = await response.text()
+    if (!body) {
+      return { exitCode: 0, stdout: "", stderr: "" }
+    }
+
+    try {
+      const parsed = JSON.parse(body) as { exitCode?: number }
+      if (typeof parsed.exitCode === "number") {
+        return { exitCode: parsed.exitCode, stdout: body, stderr: "" }
+      }
+    } catch {
+    }
+
+    return { exitCode: 0, stdout: body, stderr: "" }
+  } catch (error) {
+    const message = error instanceof Error ? error.message : String(error)
+    return { exitCode: 1, stderr: `HTTP hook error: ${message}` }
+  }
+}