fix: resolve all golangci-lint errors

Fixes 15 pre-existing lint issues:

errcheck (6 issues):
- mol_distill.go: Add _ = for f.Close() and os.Remove()
- routed.go: Add _ = for routedStorage.Close() (4 locations)

gosec (8 issues):
- maintenance.go, routes.go: Add nolint for G304 (file paths from known dirs)
- mol_distill.go: Add nolint for G304 (file creation in known search paths)
- formula.go: Change WriteFile permissions from 0644 to 0600 (G306)
- gate.go: Add nolint for G204 (exec.Command with trusted AwaitID fields)

misspell (1 issue):
- gate.go: Fix "cancelled" -> "canceled" in comment

unparam (2 issues):
- cook.go, controlflow.go: Add nolint for functions returning always-nil error

Also:
- Update pre-commit-hooks to v6.0.0
- Add lint step to "Landing the Plane" session-end protocol

.pre-commit-config.yaml

@@ -6,7 +6,7 @@ repos:
         args: [--timeout=5m]
 
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v5.0.0
+    rev: v6.0.0
     hooks:
       - id: trailing-whitespace
       - id: end-of-file-fixer