feat(examples): migrate TH-141 sample to declarative layout (WU-6)

Real-content fixture for the end-to-end pipeline. TH-141 (39 parts: 22 segment,
15 lemma, 2 example) migrated from the prototype's typst `#let parts` manifest
to ADR-0008: declarative manifest.toml (project+info+ordered parts+targets) +
per-element element.toml (kind + scalars; examples carry `source`). Content .typ
files copied byte-identical (no math corruption); per-element main.typ + meta.toml
dropped (wiring is now generated). Part order matches source exactly; 5 lemmas
have no proof.typ (optional); no cross-file imports / paralearn refs / figs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

examples/TH-141/lemmas/Girifalco-Good公式/stmt.typ

@@ -0,0 +1,7 @@
+对色散力为主的固液体系，异种相互作用能由同种相互作用能的几何平均近似：$epsilon_(S L) approx sqrt(epsilon_(S S) thin epsilon_(L L))$。相应地粘附功
+
+$ W_(S L) approx 2 sqrt(gamma_(S G) thin gamma_(L G)) . $ <Berthelot粘附>
+
+代入 @Dupré关系 得 Girifalco–Good 公式
+
+$ gamma_(S L) approx (sqrt(gamma_(S G)) - sqrt(gamma_(L G)))^2 . $ <GG公式>