feat(rules): add Rust language rules (rebased #660) (#686)

* feat(rules): add Rust coding style, hooks, and patterns rules

Add language-specific rules for Rust extending the common rule set:
- coding-style.md: rustfmt, clippy, ownership idioms, error handling,
  iterator patterns, module organization, visibility
- hooks.md: PostToolUse hooks for rustfmt, clippy, cargo check
- patterns.md: trait-based repository, newtype, enum state machines,
  builder, sealed traits, API response envelope

Rules reference existing rust-patterns skill for deep content.

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Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

* feat(rules): add Rust testing and security rules

Add remaining Rust language-specific rules:
- testing.md: cargo test, rstest parameterized tests, mockall mocking
  with mock! macro, tokio async tests, cargo-llvm-cov coverage
- security.md: secrets via env vars, parameterized SQL with sqlx,
  parse-don't-validate input validation, unsafe code audit requirements,
  cargo-audit dependency scanning, proper HTTP error status codes

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Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

* fix(rules): address review feedback on Rust rules

Fixes from Copilot, Greptile, Cubic, and CodeRabbit reviews:
- Add missing imports: use std::borrow::Cow, use anyhow::Context
- Use anyhow::Result<T> consistently (patterns.md, security.md)
- Change sqlx placeholder from ? to $1 (Postgres is most common)
- Remove Cargo.lock from hooks.md paths (auto-generated file)
- Fix tokio::test to show attribute form #[tokio::test]
- Fix mockall mock! name collision, wrap in #[cfg(test)] mod tests
- Fix --test target to match file layout (api_test, not integration)

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Co-Authored-By: Happy <yesreply@happy.engineering>

* fix: update catalog counts in README.md and AGENTS.md

Update documented counts to match actual repository state after rebase:
- Skills: 109 → 113 (new skills merged to main)
- Commands: 57 → 58 (new command merged to main)

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---------

Co-authored-by: Chris Yau <chris@diveanddev.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Happy <yesreply@happy.engineering>

rules/rust/security.md

@@ -0,0 +1,141 @@
+---
+paths:
+  - "**/*.rs"
+---
+# Rust Security
+
+> This file extends [common/security.md](../common/security.md) with Rust-specific content.
+
+## Secrets Management
+
+- Never hardcode API keys, tokens, or credentials in source code
+- Use environment variables: `std::env::var("API_KEY")`
+- Fail fast if required secrets are missing at startup
+- Keep `.env` files in `.gitignore`
+
+```rust
+// BAD
+const API_KEY: &str = "sk-abc123...";
+
+// GOOD — environment variable with early validation
+fn load_api_key() -> anyhow::Result<String> {
+    std::env::var("PAYMENT_API_KEY")
+        .context("PAYMENT_API_KEY must be set")
+}
+```
+
+## SQL Injection Prevention
+
+- Always use parameterized queries — never format user input into SQL strings
+- Use query builder or ORM (sqlx, diesel, sea-orm) with bind parameters
+
+```rust
+// BAD — SQL injection via format string
+let query = format!("SELECT * FROM users WHERE name = '{name}'");
+sqlx::query(&query).fetch_one(&pool).await?;
+
+// GOOD — parameterized query with sqlx
+// Placeholder syntax varies by backend: Postgres: $1  |  MySQL: ?  |  SQLite: $1
+sqlx::query("SELECT * FROM users WHERE name = $1")
+    .bind(&name)
+    .fetch_one(&pool)
+    .await?;
+```
+
+## Input Validation
+
+- Validate all user input at system boundaries before processing
+- Use the type system to enforce invariants (newtype pattern)
+- Parse, don't validate — convert unstructured data to typed structs at the boundary
+- Reject invalid input with clear error messages
+
+```rust
+// Parse, don't validate — invalid states are unrepresentable
+pub struct Email(String);
+
+impl Email {
+    pub fn parse(input: &str) -> Result<Self, ValidationError> {
+        let trimmed = input.trim();
+        let at_pos = trimmed.find('@')
+            .filter(|&p| p > 0 && p < trimmed.len() - 1)
+            .ok_or_else(|| ValidationError::InvalidEmail(input.to_string()))?;
+        let domain = &trimmed[at_pos + 1..];
+        if trimmed.len() > 254 || !domain.contains('.') {
+            return Err(ValidationError::InvalidEmail(input.to_string()));
+        }
+        // For production use, prefer a validated email crate (e.g., `email_address`)
+        Ok(Self(trimmed.to_string()))
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+```
+
+## Unsafe Code
+
+- Minimize `unsafe` blocks — prefer safe abstractions
+- Every `unsafe` block must have a `// SAFETY:` comment explaining the invariant
+- Never use `unsafe` to bypass the borrow checker for convenience
+- Audit all `unsafe` code during review — it is a red flag without justification
+- Prefer `safe` FFI wrappers around C libraries
+
+```rust
+// GOOD — safety comment documents ALL required invariants
+let widget: &Widget = {
+    // SAFETY: `ptr` is non-null, aligned, points to an initialized Widget,
+    // and no mutable references or mutations exist for its lifetime.
+    unsafe { &*ptr }
+};
+
+// BAD — no safety justification
+unsafe { &*ptr }
+```
+
+## Dependency Security
+
+- Run `cargo audit` to scan for known CVEs in dependencies
+- Run `cargo deny check` for license and advisory compliance
+- Use `cargo tree` to audit transitive dependencies
+- Keep dependencies updated — set up Dependabot or Renovate
+- Minimize dependency count — evaluate before adding new crates
+
+```bash
+# Security audit
+cargo audit
+
+# Deny advisories, duplicate versions, and restricted licenses
+cargo deny check
+
+# Inspect dependency tree
+cargo tree
+cargo tree -d  # Show duplicates only
+```
+
+## Error Messages
+
+- Never expose internal paths, stack traces, or database errors in API responses
+- Log detailed errors server-side; return generic messages to clients
+- Use `tracing` or `log` for structured server-side logging
+
+```rust
+// Map errors to appropriate status codes and generic messages
+// (Example uses axum; adapt the response type to your framework)
+match order_service.find_by_id(id) {
+    Ok(order) => Ok((StatusCode::OK, Json(order))),
+    Err(ServiceError::NotFound(_)) => {
+        tracing::info!(order_id = id, "order not found");
+        Err((StatusCode::NOT_FOUND, "Resource not found"))
+    }
+    Err(e) => {
+        tracing::error!(order_id = id, error = %e, "unexpected error");
+        Err((StatusCode::INTERNAL_SERVER_ERROR, "Internal server error"))
+    }
+}
+```
+
+## References
+
+See skill: `rust-patterns` for unsafe code guidelines and ownership patterns.
+See skill: `security-review` for general security checklists.