feat: add canister-security skill

.github/CODEOWNERS

@@ -24,6 +24,7 @@ package.json                     @JoshDFN @marc0olo @raymondk
 /skills/multi-canister/          @derlerd-dfinity
 /skills/stable-memory/           @derlerd-dfinity
 /skills/vetkd/                   @andreacerulli
+/skills/canister-security/       @dfinity/security
 /skills/wallet-integration/      @dfinity/oisy
 /skills/ic-dashboard/            @jp-dfinity
 

CONTRIBUTING.md

@@ -154,6 +154,7 @@ The website auto-generates from SKILL.md frontmatter — no need to edit any sou
 - **Annotate all code blocks** with language identifiers (` ```motoko `, ` ```rust `, ` ```bash `, etc.).
 - **Include canister IDs and URLs** for both local and mainnet environments.
 - **Keep it flat.** One file per skill. No nested directories, no images, no external dependencies.
+- **Don't duplicate other skills.** If another skill covers a pattern in depth (e.g., `canister-security` for access control and async safety), reference it by name in your pitfalls instead of inlining the pattern. This keeps maintenance centralized and ensures agents get the authoritative version. The `description` field is the primary mechanism agents use to discover related skills — cross-references in pitfalls serve as secondary hints.
 
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