docs(adr): commit ADR-002 (insert-mode single-source rendering + observer root + i18n post-init guard) as a repo file

[ErickXavier]

Tests added in PR #308 (tests/directives-http-pagination.test.js) reference "ADR-002 D1/D2" but no ADR-002 file exists in the repo — the ADR lives only as a Genesis EPIC comment (NOJS-295). Commit it as a proper file so the references resolve. Suggested location: docs/adr/ or .github/adr/ (repo has .github/specs and .github/reviews; pick and establish the convention). Content: the three decisions shipped in PRs #308/#304 — D1 insert-mode single-source rendering (wrapper-clone removal), D2 IntersectionObserver root = nearest scrollable ancestor (×3 observers), D3 i18n post-init guard — with context, alternatives considered, consequences, and the bundle acceptance bound (gzip ≤ 44,500 B). Reconstruct accurately from the merged PRs and their tests.

[ErickXavier]

Fixed in PR #320 → #326. ADR-002 committed at docs/adr/ADR-002-insert-mode-rendering-observer-root-i18n-guard.md (continuing from ADR-001 already in the directory): the three shipped decisions (insert-mode single-source rendering, IntersectionObserver root on all three observers, i18n post-init guard) with alternatives, consequences, and the gzip ≤ 44,500 acceptance bound. Every factual claim was source-verified during review (three spot-checks re-verified at the gate). The test references to ADR-002 D1/D2 now resolve. Verification: Jest 2232/2232; e2e 521 passed / 0 failed ×3 browsers; gzip 44,184 B ≤ 44,500. Merged to main in PR #326 (dfcf323). Ships in v1.20.1.