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/rings.go

@@ -12,12 +12,14 @@ func (g *RogueGame) ringOn() {
 	if obj == nil {
 		return
 	}
+
 	if obj.Kind != KindRing {
 		if !g.Options.Terse {
 			g.msg("it would be difficult to wrap that around a finger")
 		} else {
 			g.msg("not a ring")
 		}
+
 		return
 	}
 
@@ -27,6 +29,7 @@ func (g *RogueGame) ringOn() {
 	}
 
 	var ring int
+
 	switch {
 	case p.CurRing[Left] == nil && p.CurRing[Right] == nil:
 		if ring = g.gethand(); ring < 0 {
@@ -42,8 +45,10 @@ func (g *RogueGame) ringOn() {
 		} else {
 			g.msg("wearing two")
 		}
+
 		return
 	}
+
 	p.CurRing[ring] = obj
 
 	// Calculate the effect it has on the poor guy.
@@ -57,15 +62,18 @@ func (g *RogueGame) ringOn() {
 	}
 
 	if !g.Options.Terse {
-		g.addmsg("you are now wearing ")
+		g.addmsgf("you are now wearing ")
 	}
+
 	g.msg("%s (%c)", g.invName(obj, true), obj.PackCh)
 }
 
 // ringOff takes off a ring (rings.c ring_off).
 func (g *RogueGame) ringOff() {
 	p := &g.Player
+
 	var ring int
+
 	switch {
 	case p.CurRing[Left] == nil && p.CurRing[Right] == nil:
 		if g.Options.Terse {
@@ -73,6 +81,7 @@ func (g *RogueGame) ringOff() {
 		} else {
 			g.msg("you aren't wearing any rings")
 		}
+
 		return
 	case p.CurRing[Left] == nil:
 		ring = Right
@@ -83,12 +92,16 @@ func (g *RogueGame) ringOff() {
 			return
 		}
 	}
+
 	g.Msgs.Mpos = 0
+
 	obj := p.CurRing[ring]
 	if obj == nil {
 		g.msg("not wearing such a ring")
+
 		return
 	}
+
 	if g.dropCheck(obj) {
 		g.msg("was wearing %s(%c)", g.invName(obj, true), obj.PackCh)
 	}
@@ -102,17 +115,22 @@ func (g *RogueGame) gethand() int {
 		} else {
 			g.msg("left hand or right hand? ")
 		}
+
 		c := g.readchar()
 		if c == Escape {
 			return -1
 		}
+
 		g.Msgs.Mpos = 0
+
 		if c == 'l' || c == 'L' {
 			return Left
 		}
+
 		if c == 'r' || c == 'R' {
 			return Right
 		}
+
 		if g.Options.Terse {
 			g.msg("L or R")
 		} else {
@@ -147,6 +165,7 @@ func (g *RogueGame) ringEat(hand int) int {
 	if ring == nil {
 		return 0
 	}
+
 	eat := ringUses[ring.RingKind()]
 	if eat < 0 {
 		if g.rnd(-eat) == 0 {
@@ -155,20 +174,25 @@ func (g *RogueGame) ringEat(hand int) int {
 			eat = 0
 		}
 	}
+
 	if ring.RingKind() == RingSlowDigestion {
 		eat = -eat
 	}
+
 	return eat
 }
 
-// ringNum prints ring bonuses (rings.c ring_num).
-func ringNum(g *RogueGame, obj *Object) string {
+// ringNum prints ring bonuses (rings.c ring_num). The unused game
+// parameter keeps the nameit prfunc signature.
+func ringNum(_ *RogueGame, obj *Object) string {
 	if !obj.Flags.Has(Known) {
 		return ""
 	}
+
 	switch obj.RingKind() {
 	case RingProtection, RingAddStrength, RingIncreaseDamage, RingDexterity:
 		return fmt.Sprintf(" [%s]", num(obj.Bonus, 0, Ring))
 	}
+
 	return ""
 }