[DWAA1660]

Smoothed ink could extend beyond its raw readings, while Stroke::bounds only enclosed those readings. This put selection handles inside visible ink and let the saved SVG viewport crop a curve. In the four-reading reproduction, the outline reaches y -15.57 but the exported viewport begins at -2. The real SVG rasterizer confirms clipped pixels in both Plain and Editable exports.

Stroke::bounds now unions the original extrema with the same sampled centreline used by the painter and SVG outline. It retains the selected full-width padding, existing sheet area, and unchanged dot/two-reading behavior. Drawing::add, drawing bounds and selection bounds inherit the correction. Stored readings and pressure are unchanged. No renderer or hit-test code changes.

Fixes #231. This is separate from the cap-angle fix #218 and pressure-aware hit testing #230.

Validation

• New bounds and actual SVG-raster regressions failed before the fix, then passed.
• cargo test -p notecraft-ink: 42 existing tests and 3 new regressions passed. Cases cover rotation, reversal, all tools, pressure, full-width padding, existing sheet area, selection bounds and stable Editable rereading.
• cargo test -p notecraft-ui-egui --test ink_svg_bounds: passed. It uses the existing SVG loader for real Plain/Editable exports, with an expanded-viewport control whose paths and readings are identical.
• cargo xtask demo and cargo xtask demo-check: passed; generation produced no tracked notebook changes, and all 662 generated files match the source.
• cargo test -p notecraft-formats --test format_parity: 3 passed.
• Diagnostic Plain/Editable renders were reviewed. The reproduction loses 64 opaque pixels before the fix and zero after; both flavours render identically.
• Enabled commit hooks passed. The normal push retains the repository's required full pre-push gate.

Hosted platform, coverage and WASM results will be reported by CI. No new dependencies or test doubles were added.

The normal pre-push gate completed successfully: cargo xtask ci reported all checks passed.