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/GGZ浸润判据/stmt.typ

@@ -0,0 +1,5 @@
+把 Berthelot 估计 @GG公式 代回 Young 方程 @Young方程，得到 Girifalco–Good–Zisman 浸润判据
+
+$ cos theta = 2 sqrt(gamma_(S G) / gamma_(L G)) - 1 . $ <GGZ判据>
+
+接触角完全由比值 $gamma_(S G) \/ gamma_(L G)$ 一个无量纲数决定。