Add docs/references/data/database-construction.md as the single home for how the SQLite DB is built and evolved: boot init order, drizzle migrations (regenerate-never-rename, CI gates, additive-vs-rebuild), the CUSTOM_SQL_STATEMENTS every-boot replay (~0.1ms O(1)), and the FTS5 fts_rowid rowid-stability rule, plus a gotchas table. Move the Migrations and Custom SQL sections out of database-patterns.md into it (left as pointers), and index it from data/README.md and src/main/data/db/README.md.
Fix stale references found while consolidating: wrong generate command, customSql.ts vs customSqls.ts, columnHelpers.ts vs _columnHelpers.ts, a nonexistent messageFts.ts, yarn vs pnpm, the v2-todo single-0000 claim, the generated-column wording, and v1 data.blocks vocabulary in the testing doc.
