fix: Dockerfile stub binary not replaced, design system rules

- remove stub colony binary after dep cache so cargo rebuilds with real source
- expand .claude/rules/frontend.md with full design system enforcement
- mandatory: semantic tokens, shadcn components, Tailwind only, mobile-first
- forbidden: inline styles, custom CSS, arbitrary colors, raw HTML elements

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infra/colony/Dockerfile

@@ -20,9 +20,10 @@ RUN mkdir -p crates/colony-types/src crates/colony/src \
     && echo "fn main() {}" > crates/colony/src/main.rs \
     && echo "" > crates/colony-types/src/lib.rs \
     && cargo build --release -p colony 2>/dev/null || true \
+    && rm -rf target/release/colony target/release/deps/colony-* \
     && rm crates/colony/src/main.rs crates/colony-types/src/lib.rs
 
-# Now copy real source and build (deps already cached)
+# Now copy real source and build (deps already cached, binary removed so cargo rebuilds)
 COPY crates/ crates/
 RUN cargo build --release -p colony