chore(lint): adopt canonical golangci-lint config

Replace .golangci.yml with the shared canonical config. The old
config's top-level linters-settings block was silently ignored under
the v2 schema, so the lll/funlen/cyclop/dupl thresholds now actually
apply. The four repo-specific disables (mnd, exhaustive, paralleltest,
testpackage) move out of the config into targeted in-code nolint
directives carrying their original approval dates, keeping the config
byte-identical to the canonical one.

Fixes surfaced by the stricter settings: t.Parallel() added to all 32
tests, 24 overlong lines wrapped or their comments tightened, tcell
control-code returns rewritten as character literals, dupl markers on
the identically-shaped item data tables, and two wsl_v5 defer cuddles.

No behavior changes. The repo has no golangci-lint version pin (no
Dockerfile or CI; make lint runs the host binary, currently v2.12.2),
so there was nothing to bump.

game/newlevel_test.go

@@ -1,3 +1,4 @@
+//nolint:testpackage // white-box tests reach unexported state (approved 2026-07-07)
 package game
 
 import (
@@ -35,6 +36,8 @@ func renderMap(g *RogueGame) string {
 }
 
 func TestNewLevelInvariants(t *testing.T) {
+	t.Parallel()
+
 	for _, seed := range []int32{1, 12345, 2026, 99999} {
 		g := genLevel(t, seed)
 
@@ -142,6 +145,8 @@ func checkStartingKit(t *testing.T, g *RogueGame, seed int32) {
 }
 
 func TestNewLevelDeterministic(t *testing.T) {
+	t.Parallel()
+
 	a := renderMap(genLevel(t, 12345))
 
 	b := renderMap(genLevel(t, 12345))
@@ -158,6 +163,8 @@ func TestNewLevelDeterministic(t *testing.T) {
 // TestDeeperLevels exercises generation across many depths and seeds —
 // mazes, dark rooms, traps, treasure rooms — as a crash/invariant sweep.
 func TestDeeperLevels(t *testing.T) {
+	t.Parallel()
+
 	for _, seed := range []int32{7, 42, 1000, 31337} {
 		g := New(Params{Seed: seed})
 		for depth := 1; depth <= 30; depth++ {