Two Windows-install regressions on top of 1.2.5:

1. better-sqlite3@^11.7.0 has no Node 24 (NODE_MODULE_VERSION 137)
   win32-x64 prebuild, so npm fell back to `node-gyp rebuild` which
   needs Visual Studio. Bumped to ^12.10.0 in both the root and
   packages/coworker-memory; v12.10.0 ships a v137 prebuild and
   installs cleanly without a C++ toolchain.

2. exceljs@4.4.0 was generating eight `npm warn deprecated` lines on
   every install — glob@7 (CVE), inflight (memory leak), rimraf@2,
   fstream, lodash.isequal, plus old uuid. Upstream is dormant
   (last commit Jan 2024). Dropped exceljs entirely from the
   scratchpad data-lib bindings; cell code that called
   `new ExcelJS.Workbook()` will now ReferenceError. xlsx-capability
   replacement (likely xlsx-populate@1.21.0) tracked in the
   coworker roadmap § Out-of-scope.

Touches: root + workspace package.jsons, kernel-bindings.ts,
kernel-entry.ts, scratchpad-tool.ts prompt strings, two test files,
CHANGELOG.md (new 1.2.6 entry), coworker-roadmap.md (new entry).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>