feat: add web search and background process tools (Phases 4-5)

Phase 4 - Web search tool:
- Brave Search API + SearXNG fallback
- Configurable provider, max results
- 14 tests

Phase 5 - Background process management:
- ProcessManager with start/status/output/kill/list tools
- Configurable max concurrent, max runtime, buffer size
- 28 tests

src/tools/builtin/process/output.ts

@@ -0,0 +1,36 @@
+import type { Tool, ToolResult } from '../../types.js';
+import type { ProcessManager } from './manager.js';
+
+interface ProcessOutputArgs {
+  id: string;
+}
+
+export function createProcessOutputTool(manager: ProcessManager): Tool {
+  return {
+    name: 'process.output',
+    description: 'Read recent stdout/stderr output from a background process. Returns the last ~64KB of output.',
+    inputSchema: {
+      type: 'object',
+      properties: {
+        id: { type: 'string', description: 'Process ID (e.g. "proc_1")' },
+      },
+      required: ['id'],
+    },
+    execute: async (rawArgs: unknown): Promise<ToolResult> => {
+      const args = rawArgs as ProcessOutputArgs;
+      try {
+        const output = manager.getOutput(args.id);
+        if (!output) {
+          return { success: true, output: '(no output yet)' };
+        }
+        return { success: true, output };
+      } catch (error) {
+        return {
+          success: false,
+          output: '',
+          error: error instanceof Error ? error.message : 'Failed to get process output',
+        };
+      }
+    },
+  };
+}