feat(parser): strip leading stop-words (at, the, a, an) from noun phrase

Allows `look at lamp`, `examine the letter`, `take a key`, `take an oil lamp`.
Stop-words are only removed from the head of the noun phrase, not from
anywhere in the middle.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/engine/parser.ts

@@ -59,6 +59,9 @@ const VERB_ONLY_VERBS = new Set<string>(['look', 'inventory', 'wait'])
 /** Two-word verb prefixes (e.g. "pick up X"). */
 const TWO_WORD_VERBS = ['pick up']
 
+/** Leading stop-words stripped from the noun phrase before matching. */
+const STOP_WORDS = new Set(['at', 'the', 'a', 'an'])
+
 function tokenize(input: string): string[] {
   return input.trim().toLowerCase().split(/\s+/).filter(Boolean)
 }
@@ -126,6 +129,11 @@ export function parse(rawInput: string, ctx: ParserContext): ParsedCommand {
     return { kind: 'unknown', raw: trimmed, reason: 'unknown-verb' }
   }
 
+  // Strip leading stop-words from the noun phrase (e.g. "at", "the", "a", "an").
+  while (rest.length > 0 && STOP_WORDS.has(rest[0]!)) {
+    rest = rest.slice(1)
+  }
+
   if (rest.length === 0) {
     if (VERB_ONLY_VERBS.has(verb)) {
       return { kind: 'verb-only', verb: verb as 'look' | 'inventory' | 'wait' }