chore(lint): exclude upstream rrule-go's lno1wkst dead store, narrowly (TASK-4100)

golangci-lint's ineffassign flags `lno1wkst = 0` in the vendored
internal/schedule/internal/rrule/rrule.go. The line is upstream v1.8.2,
verbatim since the import commit. Exclude that one finding (path, linter
and text) rather than edit upstream code or unlint the whole package, so
every other linter still checks our budget/stall delta in the same file.
PROVENANCE.md records the exclusion.

Claude-Session: https://claude.ai/code/session_01Pa22hHpfXoZbQkEFvPtNeS

.golangci.yml

@@ -40,6 +40,15 @@ linters:
       - ^docs/
       - ^deploy/
       - ^skills/
+    rules:
+      # Upstream rrule-go v1.8.2's own dead store (`lno1wkst = 0`), vendored
+      # verbatim. Excluded narrowly instead of editing upstream code, so every
+      # other linter still checks our budget/stall delta in the same file
+      # (TASK-4100 lint ruling; see the package's PROVENANCE.md).
+      - path: ^internal/schedule/internal/rrule/rrule\.go$
+        linters:
+          - ineffassign
+        text: lno1wkst
 
 formatters:
   enable:

internal/schedule/internal/rrule/PROVENANCE.md

@@ -25,6 +25,10 @@ The differences from upstream marked TASK-4100 in rrule.go are:
 rruleset.go, str.go, util.go and LICENSE are byte-identical to upstream: their
 sha256 matches the table below. rrule.go is the only modified file.
 
+Lint: .golangci.yml excludes one upstream finding, ineffassign on `lno1wkst = 0`
+in rrule.go (upstream's own dead store), rather than editing upstream code. Every
+other linter still runs on this package, including our delta (TASK-4100 lint ruling).
+
 ## File count
 
 The brief for this work said 3 library files; there are 4 (rrule.go, rruleset.go,