Adopt house golangci-lint config; fix all approved-linter findings

.golangci.yml is the prompts-repo standard verbatim plus one approved
exception (paralleltest, sneak 2026-07-06). Roughly 1,500 findings
fixed:

- autofix sweep (wsl_v5/nlreturn/intrange/modernize formatting), with
  the misspell autofix REVERTED where it rewrote authentic C game text
  ("missle vanishes" stays, with nolint and a comment)
- error handling: errcheck sites get real handling — saveFile now
  closes explicitly and removes corrupt saves, scoreboard writes are
  documented best-effort, err113 sentinel errors (ErrSaveOutOfDate,
  ErrScreenTooSmall); panics allowed for unrecoverable states per
  MEMORY.md policy
- gosec: real fixes (ParseInt for SEED, 0600 scorefile) and justified
  per-line nolints for provably-bounded conversions (randomMonsterLetter
  helper collapses eight rnd(26)+'A' sites)
- API tidying from linters: pointer receivers on flag types
  (recvcheck), msg helpers renamed addmsgf/doaddf/Printwf/MvPrintwf
  (goprintffuncname), myExit()/findFloor(monst)/mkGameInput(t) drop
  always-constant params (unparam), gameEnd carries no status
- gocritic/staticcheck: if-else chains to switches, the pack.c
  inventory filter untangled into matchesFilter, main.go split so
  defers run before exit (exitAfterDefer, funlen)
- revive doc comments on all exported flag types/consts/methods

Remaining findings are confined to linters pending sneak's exception
decision (mnd, gochecknoglobals, cyclop, nestif, gocognit, exhaustive,
goconst, testpackage); TODO.md records the state. MEMORY.md added at
repo root as the project's agent working notes.

game/newlevel_test.go

@@ -7,24 +7,30 @@ import (
 
 func genLevel(t *testing.T, seed int32) *RogueGame {
 	t.Helper()
+
 	g := NewGame(Config{Seed: seed})
 	g.NewLevel()
+
 	return g
 }
 
 // renderMap draws the raw level map (not the screen) as text.
 func renderMap(g *RogueGame) string {
 	var sb strings.Builder
-	for y := 0; y < NumLines; y++ {
-		for x := 0; x < NumCols; x++ {
+
+	for y := range NumLines {
+		for x := range NumCols {
 			ch := g.Level.Char(y, x)
 			if m := g.Level.MonsterAt(y, x); m != nil {
 				ch = m.Type
 			}
+
 			sb.WriteByte(ch)
 		}
+
 		sb.WriteByte('\n')
 	}
+
 	return sb.String()
 }
 
@@ -44,9 +50,11 @@ func TestNewLevelInvariants(t *testing.T) {
 			t.Errorf("seed %d: hero on unwalkable cell %q", seed,
 				g.Level.Char(hp.Y, hp.X))
 		}
+
 		if g.Level.MonsterAt(hp.Y, hp.X) != nil {
 			t.Errorf("seed %d: hero standing on a monster", seed)
 		}
+
 		if g.Player.Room == nil {
 			t.Errorf("seed %d: hero not in any room", seed)
 		}
@@ -56,6 +64,7 @@ func TestNewLevelInvariants(t *testing.T) {
 		if !strings.Contains(m, "|") || !strings.Contains(m, "-") {
 			t.Errorf("seed %d: no room walls drawn", seed)
 		}
+
 		if !strings.Contains(m, ".") && !strings.Contains(m, "#") {
 			t.Errorf("seed %d: no floor or passages drawn", seed)
 		}
@@ -66,6 +75,7 @@ func TestNewLevelInvariants(t *testing.T) {
 				t.Errorf("seed %d: monster %c not indexed at its position",
 					seed, mon.Type)
 			}
+
 			if mon.Room == nil {
 				t.Errorf("seed %d: monster %c has no room", seed, mon.Type)
 			}
@@ -87,10 +97,12 @@ func TestNewLevelInvariants(t *testing.T) {
 			t.Errorf("seed %d: starting pack has %d items, want 5",
 				seed, len(g.Player.Pack))
 		}
+
 		if g.Player.CurWeapon == nil ||
 			g.Player.CurWeapon.WeaponKind() != WeaponMace {
 			t.Errorf("seed %d: not wielding the starting mace", seed)
 		}
+
 		if g.Player.CurArmor == nil ||
 			g.Player.CurArmor.ArmorKind() != ArmorRingMail {
 			t.Errorf("seed %d: not wearing the starting ring mail", seed)
@@ -100,10 +112,12 @@ func TestNewLevelInvariants(t *testing.T) {
 
 func TestNewLevelDeterministic(t *testing.T) {
 	a := renderMap(genLevel(t, 12345))
+
 	b := renderMap(genLevel(t, 12345))
 	if a != b {
 		t.Error("same seed produced different levels")
 	}
+
 	c := renderMap(genLevel(t, 54321))
 	if a == c {
 		t.Error("different seeds produced identical levels")
@@ -118,6 +132,7 @@ func TestDeeperLevels(t *testing.T) {
 		for depth := 1; depth <= 30; depth++ {
 			g.Depth = depth
 			g.NewLevel()
+
 			st := g.Level.Stairs
 			if g.Level.Char(st.Y, st.X) != Stairs {
 				t.Fatalf("seed %d depth %d: missing staircase", seed, depth)