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.

term/tcell.go

@@ -128,6 +128,7 @@ func namedKey(k tcell.Key) (byte, bool) {
 // motionKey translates the arrow and paging keys to Rogue's movement
 // letters (tcell.go ReadChar).
 func motionKey(k tcell.Key) (byte, bool) {
+	//nolint:exhaustive // translation table: all other keys fall through
 	switch k {
 	case tcell.KeyUp:
 		return 'k', true
@@ -153,19 +154,20 @@ func motionKey(k tcell.Key) (byte, bool) {
 // editingKey translates the editing and control keys to their C0 codes
 // (tcell.go ReadChar).
 func editingKey(k tcell.Key) (byte, bool) {
+	//nolint:exhaustive // translation table: all other keys fall through
 	switch k {
 	case tcell.KeyEnter:
 		return '\n', true
 	case tcell.KeyEscape:
 		return game.Escape, true
 	case tcell.KeyBackspace, tcell.KeyBackspace2:
-		return 8, true
+		return '\b', true
 	case tcell.KeyDelete:
-		return 0x7f, true
+		return '\x7f', true
 	case tcell.KeyTab:
 		return '\t', true
 	case tcell.KeyCtrlC:
-		return 3, true
+		return '\x03', true
 	}
 
 	return 0, false
@@ -188,8 +190,8 @@ func (t *Tcell) ShellEscape() {
 		"[Entering shell; exit to return to the game]")
 
 	// The shell session has no deadline by design; Background context.
-	cmd := exec.CommandContext(context.Background(), //nolint:gosec // G204: the user's own $SHELL
-		shell)
+	//nolint:gosec // G204: the user's own $SHELL
+	cmd := exec.CommandContext(context.Background(), shell)
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr