feat: add text adventure shell (PLAN.md 3.4)

Zork-style dungeon crawler set in an abandoned data center / medieval dungeon.
11 rooms, 6 items, 3 puzzles (dark room, locked door, maintenance panel),
standard text adventure parser with verb aliases and direction shortcuts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/shell/adventure/parser.go

@@ -0,0 +1,106 @@
+package adventure
+
+import "strings"
+
+type parsedCommand struct {
+	verb   string
+	object string
+}
+
+// directionAliases maps shorthand and full direction names to canonical forms.
+var directionAliases = map[string]string{
+	"n":     "north",
+	"s":     "south",
+	"e":     "east",
+	"w":     "west",
+	"u":     "up",
+	"d":     "down",
+	"north": "north",
+	"south": "south",
+	"east":  "east",
+	"west":  "west",
+	"up":    "up",
+	"down":  "down",
+}
+
+// verbAliases maps aliases to canonical verbs.
+var verbAliases = map[string]string{
+	"look":    "look",
+	"l":       "look",
+	"examine": "look",
+	"inspect": "look",
+	"x":       "look",
+	"go":      "go",
+	"move":    "go",
+	"walk":    "go",
+	"take":    "take",
+	"get":     "take",
+	"grab":    "take",
+	"pick":    "take",
+	"drop":    "drop",
+	"put":     "drop",
+	"use":     "use",
+	"apply":   "use",
+	"inventory": "inventory",
+	"inv":       "inventory",
+	"i":         "inventory",
+	"help":      "help",
+	"?":         "help",
+	"quit":      "quit",
+	"exit":      "quit",
+	"logout":    "quit",
+	"q":         "quit",
+}
+
+// articles are stripped from input.
+var articles = map[string]bool{
+	"the": true,
+	"a":   true,
+	"an":  true,
+}
+
+// parseCommand parses raw input into a verb and object.
+func parseCommand(input string) parsedCommand {
+	input = strings.TrimSpace(strings.ToLower(input))
+	if input == "" {
+		return parsedCommand{}
+	}
+
+	words := strings.Fields(input)
+
+	// Strip articles.
+	var filtered []string
+	for _, w := range words {
+		if !articles[w] {
+			filtered = append(filtered, w)
+		}
+	}
+	if len(filtered) == 0 {
+		return parsedCommand{}
+	}
+
+	first := filtered[0]
+
+	// Bare direction → go <direction>.
+	if dir, ok := directionAliases[first]; ok {
+		return parsedCommand{verb: "go", object: dir}
+	}
+
+	// Known verb alias.
+	if verb, ok := verbAliases[first]; ok {
+		object := ""
+		if len(filtered) > 1 {
+			object = strings.Join(filtered[1:], " ")
+			// Resolve direction alias in object for "go north" etc.
+			if verb == "go" {
+				if dir, ok := directionAliases[object]; ok {
+					object = dir
+				}
+			}
+		}
+		return parsedCommand{verb: verb, object: object}
+	}
+
+	// Unknown verb — return as-is so game can give an error.
+	return parsedCommand{verb: first, object: strings.Join(filtered[1:], " ")}
+}