chore: scrub dangling references to deleted specs/plans from sources

docs/specs and docs/plans were retired (prior commit); the source/test
comments that cited them ("spec 0050 §4.1", "spec §Testing N", "per spec",
"the spec's ...") now point at nothing. Strip every such pointer while
preserving the technical substance, the design-ledger contract refs
(C1/C11/C20/C34/C12.1/...), and the Gitea issue refs (#41).

Comment/doc edits only across 20 files — no logic change; full workspace
suite green, clippy clean.

crates/aura-cli/src/render.rs

@@ -88,7 +88,7 @@ mod tests {
     /// deterministic model as the viewer's data source, carries the Graphviz-WASM
     /// bootstrap, and keeps the C4 four-colour palette. Structural, not pixel:
     /// the DOT/SVG are Graphviz-version-dependent and are exercised by hand
-    /// against the prototype (spec Testing strategy).
+    /// against the prototype.
     #[test]
     fn render_html_is_self_contained_and_embeds_the_model() {
         let html = render_html(&sample_blueprint());