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/rng.go

@@ -11,21 +11,17 @@ type Rng struct {
 	Seed int32
 }
 
-// next steps the generator and returns the next raw value (the RN macro).
-func (r *Rng) next() int {
-	r.Seed = r.Seed*11109 + 13849
-	return int(r.Seed>>16) & 0xffff
-}
-
 // Rnd picks a very random number in [0, rng) (main.c rnd).
 func (r *Rng) Rnd(rng int) int {
 	if rng == 0 {
 		return 0
 	}
+
 	v := r.next()
 	if v < 0 {
 		v = -v
 	}
+
 	return v % rng
 }
 
@@ -35,9 +31,17 @@ func (r *Rng) Roll(number, sides int) int {
 	for ; number > 0; number-- {
 		dtotal += r.Rnd(sides) + 1
 	}
+
 	return dtotal
 }
 
+// next steps the generator and returns the next raw value (the RN macro).
+func (r *Rng) next() int {
+	r.Seed = r.Seed*11109 + 13849
+
+	return int(r.Seed>>16) & 0xffff
+}
+
 // rnd is the ported code's spelling of C rnd(): every call site in the C
 // sources reads rnd(x), and keeping that shape makes cross-checking easy.
 func (g *RogueGame) rnd(rng int) int { return g.Rng.Rnd(rng) }