add \$B memory command

Registers 'memory' in META_COMMANDS, wires the meta-command dispatch
to a lazy-imported handler in memory-command.ts. Lazy because the
import graph (cdp-bridge + memory-snapshot + buffer accessors) isn't
useful to projects that never run the diagnostic.

The handler assembles MemoryStructureStats from the modules that own
each buffer (cdp-inspector mod history stats, activity subscriber
count, console/network/dialog buffer lengths, captureBuffer bytes,
inspectorSubscriber count via a new server.ts export) and calls
BrowserManager.getMemorySnapshot. Output is text by default, JSON with
--json so the sidebar footer and test harness can consume it
programmatically. buildMemorySnapshotJson is the entry the /memory
endpoint will call in the next commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

browse/src/commands.ts

@@ -45,6 +45,7 @@ export const META_COMMANDS = new Set([
   'domain-skill',
   'skill',
   'cdp',
+  'memory',
 ]);
 
 export const ALL_COMMANDS = new Set([...READ_COMMANDS, ...WRITE_COMMANDS, ...META_COMMANDS]);
@@ -89,6 +90,7 @@ export function wrapUntrustedContent(result: string, url: string): string {
 
 export const COMMAND_DESCRIPTIONS: Record<string, { category: string; description: string; usage?: string }> = {
   // Navigation
+  'memory':  { category: 'Diagnostics', description: 'Snapshot Bun heap + per-tab JS heap + Chromium process tree + bounded buffer sizes. JSON output with --json.', usage: 'memory [--json]' },
   'goto':    { category: 'Navigation', description: 'Navigate to URL (http://, https://, or file:// scoped to cwd/TEMP_DIR)', usage: 'goto <url>' },
   'load-html': { category: 'Navigation', description: 'Load HTML via setContent. Accepts a file path under safe-dirs (validated), OR --from-file <payload.json> with {"html":"...","waitUntil":"..."} for large inline HTML (Windows argv safe).', usage: 'load-html <file> [--wait-until load|domcontentloaded|networkidle] [--tab-id <N>]  |  load-html --from-file <payload.json> [--tab-id <N>]' },
   'back':    { category: 'Navigation', description: 'History back' },