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/seedcompat_test.go

@@ -1,3 +1,4 @@
+//nolint:testpackage // white-box tests reach unexported state (approved 2026-07-07)
 package game
 
 import (
@@ -51,6 +52,8 @@ func dumpItemTables(seed int32, g *RogueGame) string {
 // match C byte for byte. The golden is captured from an instrumented build
 // of the C game (testdata/README.md).
 func TestSeedCompatItemTables(t *testing.T) {
+	t.Parallel()
+
 	golden, err := os.ReadFile("testdata/item_tables.golden")
 	if err != nil {
 		t.Fatalf("read golden: %v", err)