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.

MEMORY.md

@@ -0,0 +1,40 @@
+# Project Memory
+
+Working notes for agents on this repo. Read this alongside TODO.md
+(which holds the step queue and workflow) before starting work.
+
+## Error handling
+
+Panicking on bad/unexpected errors is allowed and preferred over
+threading unlikely error returns through game code — e.g. write-side
+Close/encode failures where continuing would mean corrupt state. The
+game already unwinds C's exit() calls via a gameEnd panic recovered in
+Run. Return errors where a caller genuinely handles them (save-file
+prompts, restore validation). Reserve deliberate `_ =` discards for
+true best-effort paths (scorefile writes, signal-time autosave), always
+with a comment saying why.
+
+## Linting
+
+The .golangci.yml is the house standard and may only be modified with
+sneak's explicit permission. To disable a linter, ask, explaining what
+the linter does; he approves specific exceptions, which are recorded
+in the config's "Repo-specific exceptions" block with the approval
+date. Approved so far: paralleltest (2026-07-06). Line-level //nolint
+with a reason is used sparingly for C-faithfulness (e.g. the authentic
+"missle" message spellings) and provably-safe gosec conversions; each
+needs a justifying comment.
+
+## Faithfulness
+
+Behavior must not change during the idiomatic-Go refactor unless a
+TODO step says so. The 80x24 seed-compatible gameplay, message text
+(including original typos), RNG call order, and C quirks (documented
+in tests like TestHoldScrollGreedyMonsterQuirk) are contract. Doc
+comments keep their "(file.c func_name)" breadcrumbs.
+
+## Debugging
+
+Write real, committed test files with t.Logf output and run plain
+`go test -v`; no throwaway scratch scripts. Successful debug probes
+become regression tests.