P5: track index.d.ts + reject invalid periods in the Node binding (#83)

* build(node): track the generated index.d.ts (P5.1)

index.js was committed but index.d.ts was gitignored, an inconsistency that
also contradicts CONTRIBUTING ('regenerate both .d.ts/.js when a binding API
changes'). Track index.d.ts too so the repo carries the TypeScript types as a
matched pair with index.js. Generated by napi build; ~214 indicator classes.

* fix(node): reject invalid periods instead of clamping them (P5.4)

The Node scalar-indicator macro clamped period 0 to 1 (via clamp_period + must)
and the multi-parameter constructors did the same, silently swallowing the
core's PeriodZero validation. The core rejects period 0 (Error::PeriodZero),
and the Python and WASM bindings already propagate it — Node was the outlier,
masking caller mistakes. Make the macro constructor fallible and let every
constructor propagate the core error via map_err, removing clamp_period/must.
Update the smoke test (period 0 now throws, matching core/Python/WASM).

* docs(changelog): note the Node period-validation change (P5.4)

Behavior change per CONTRIBUTING: Node constructors now reject invalid periods
instead of clamping. Add an [Unreleased] Changed entry.

* chore: drop accidentally committed scratch log

.gitignore

@@ -44,8 +44,10 @@ tarpaulin-report.html
 # Node binding artifacts
 **/node_modules/
 bindings/node/*.node
-bindings/node/index.d.ts
 bindings/node/npm-debug.log*
+# index.js + index.d.ts are generated by `napi build` but committed (a matched
+# pair) so consumers and the repo get TypeScript types; CONTRIBUTING requires
+# regenerating both when a binding's public API changes.
 # package-lock.json is committed for the tracked Node packages — bindings/node/
 # and examples/node/ — so contributors get reproducible npm installs. There is
 # no top-level npm package, and the ghost-ignored site/ keeps its lockfile local.