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_test.go

@@ -46,6 +46,7 @@ func TestRndZeroDoesNotStep(t *testing.T) {
 	if got := r.Rnd(0); got != 0 {
 		t.Fatalf("rnd(0) = %d, want 0", got)
 	}
+
 	if r.Seed != 42 {
 		t.Fatalf("rnd(0) stepped the generator: seed = %d, want 42", r.Seed)
 	}
@@ -58,6 +59,7 @@ func TestSpreadSmallValues(t *testing.T) {
 	if got := g.spread(1); got != 1 {
 		t.Errorf("spread(1) = %d, want 1", got)
 	}
+
 	if got := g.spread(2); got != 2 {
 		t.Errorf("spread(2) = %d, want 2", got)
 	}