feat: add cache module with moka-backed post/tag/stats caching

- Create src/cache.rs with CacheKey enum, moka cache instances,
  getter/setter functions, and invalidation helpers.
- TTLs: post list 60s, tags 300s, single post 600s, stats 60s,
  tag posts 120s.
- Register mod cache in src/main.rs.
- All cache internals gated behind #[cfg(feature = "server")]

src/cache.rs

@@ -0,0 +1,210 @@
+#[cfg(feature = "server")]
+use moka::future::Cache;
+#[cfg(feature = "server")]
+use std::sync::LazyLock;
+#[cfg(feature = "server")]
+use std::time::Duration;
+
+use crate::models::post::{Post, PostStats, Tag};
+
+// ============================================================================
+// Cache TTL Configuration
+// ============================================================================
+
+#[cfg(feature = "server")]
+const TTL_POST_LIST: Duration = Duration::from_secs(60);
+#[cfg(feature = "server")]
+const TTL_TAG_LIST: Duration = Duration::from_secs(300);
+#[cfg(feature = "server")]
+const TTL_SINGLE_POST: Duration = Duration::from_secs(600);
+#[cfg(feature = "server")]
+const TTL_POST_STATS: Duration = Duration::from_secs(60);
+#[cfg(feature = "server")]
+const TTL_TAG_POSTS: Duration = Duration::from_secs(120);
+
+// ============================================================================
+// Cache Key Types
+// ============================================================================
+
+#[derive(Debug, Clone, Hash, Eq, PartialEq)]
+pub enum CacheKey {
+    PublishedPosts { page: i32, per_page: i32 },
+    AllTags,
+    PostBySlug(String),
+    PostsByTag(String),
+    PostStats,
+}
+
+impl CacheKey {
+    pub fn as_string(&self) -> String {
+        match self {
+            CacheKey::PublishedPosts { page, per_page } => {
+                format!("posts:list:{}:{}", page, per_page)
+            }
+            CacheKey::AllTags => "tags:all".to_string(),
+            CacheKey::PostBySlug(slug) => format!("post:slug:{}", slug),
+            CacheKey::PostsByTag(tag) => format!("posts:tag:{}", tag),
+            CacheKey::PostStats => "posts:stats".to_string(),
+        }
+    }
+}
+
+// ============================================================================
+// Cache Instances
+// ============================================================================
+
+#[cfg(feature = "server")]
+pub type PostListCache = Cache<String, Vec<Post>>;
+
+#[cfg(feature = "server")]
+pub type TagListCache = Cache<String, Vec<Tag>>;
+
+#[cfg(feature = "server")]
+pub type SinglePostCache = Cache<String, Option<Post>>;
+
+#[cfg(feature = "server")]
+pub type PostStatsCache = Cache<String, PostStats>;
+
+#[cfg(feature = "server")]
+static POST_LIST_CACHE: LazyLock<PostListCache> = LazyLock::new(|| {
+    Cache::builder()
+        .max_capacity(100)
+        .time_to_live(TTL_POST_LIST)
+        .build()
+});
+
+#[cfg(feature = "server")]
+static TAG_LIST_CACHE: LazyLock<TagListCache> = LazyLock::new(|| {
+    Cache::builder()
+        .max_capacity(50)
+        .time_to_live(TTL_TAG_LIST)
+        .build()
+});
+
+#[cfg(feature = "server")]
+static SINGLE_POST_CACHE: LazyLock<SinglePostCache> = LazyLock::new(|| {
+    Cache::builder()
+        .max_capacity(200)
+        .time_to_live(TTL_SINGLE_POST)
+        .build()
+});
+
+#[cfg(feature = "server")]
+static POST_STATS_CACHE: LazyLock<PostStatsCache> = LazyLock::new(|| {
+    Cache::builder()
+        .max_capacity(10)
+        .time_to_live(TTL_POST_STATS)
+        .build()
+});
+
+#[cfg(feature = "server")]
+static TAG_POSTS_CACHE: LazyLock<PostListCache> = LazyLock::new(|| {
+    Cache::builder()
+        .max_capacity(100)
+        .time_to_live(TTL_TAG_POSTS)
+        .build()
+});
+
+// ============================================================================
+// Public Cache API
+// ============================================================================
+
+#[cfg(feature = "server")]
+pub async fn get_post_list(key: &CacheKey) -> Option<Vec<Post>> {
+    POST_LIST_CACHE.get(&key.as_string()).await
+}
+
+#[cfg(feature = "server")]
+pub async fn set_post_list(key: &CacheKey, posts: Vec<Post>) {
+    let _ = POST_LIST_CACHE.insert(key.as_string(), posts).await;
+}
+
+#[cfg(feature = "server")]
+pub async fn get_tag_list() -> Option<Vec<Tag>> {
+    TAG_LIST_CACHE.get(&CacheKey::AllTags.as_string()).await
+}
+
+#[cfg(feature = "server")]
+pub async fn set_tag_list(tags: Vec<Tag>) {
+    let _ = TAG_LIST_CACHE.insert(CacheKey::AllTags.as_string(), tags).await;
+}
+
+#[cfg(feature = "server")]
+pub async fn get_post_by_slug(slug: &str) -> Option<Option<Post>> {
+    SINGLE_POST_CACHE.get(&CacheKey::PostBySlug(slug.to_string()).as_string()).await
+}
+
+#[cfg(feature = "server")]
+pub async fn set_post_by_slug(slug: &str, post: Option<Post>) {
+    let _ = SINGLE_POST_CACHE
+        .insert(CacheKey::PostBySlug(slug.to_string()).as_string(), post)
+        .await;
+}
+
+#[cfg(feature = "server")]
+pub async fn get_posts_by_tag(tag: &str) -> Option<Vec<Post>> {
+    TAG_POSTS_CACHE
+        .get(&CacheKey::PostsByTag(tag.to_string()).as_string())
+        .await
+}
+
+#[cfg(feature = "server")]
+pub async fn set_posts_by_tag(tag: &str, posts: Vec<Post>) {
+    let _ = TAG_POSTS_CACHE
+        .insert(CacheKey::PostsByTag(tag.to_string()).as_string(), posts)
+        .await;
+}
+
+#[cfg(feature = "server")]
+pub async fn get_post_stats() -> Option<PostStats> {
+    POST_STATS_CACHE.get(&CacheKey::PostStats.as_string()).await
+}
+
+#[cfg(feature = "server")]
+pub async fn set_post_stats(stats: PostStats) {
+    let _ = POST_STATS_CACHE
+        .insert(CacheKey::PostStats.as_string(), stats)
+        .await;
+}
+
+// ============================================================================
+// Cache Invalidation
+// ============================================================================
+
+#[cfg(feature = "server")]
+pub async fn invalidate_post_lists() {
+    POST_LIST_CACHE.invalidate_all();
+}
+
+#[cfg(feature = "server")]
+pub async fn invalidate_all_tags() {
+    TAG_LIST_CACHE.invalidate_all();
+}
+
+#[cfg(feature = "server")]
+pub async fn invalidate_post_by_slug(slug: &str) {
+    SINGLE_POST_CACHE
+        .invalidate(&CacheKey::PostBySlug(slug.to_string()).as_string())
+        .await;
+}
+
+#[cfg(feature = "server")]
+pub async fn invalidate_posts_by_tag(tag: &str) {
+    TAG_POSTS_CACHE
+        .invalidate(&CacheKey::PostsByTag(tag.to_string()).as_string())
+        .await;
+}
+
+#[cfg(feature = "server")]
+pub async fn invalidate_post_stats() {
+    POST_STATS_CACHE.invalidate_all();
+}
+
+#[cfg(feature = "server")]
+pub async fn invalidate_all_post_caches() {
+    POST_LIST_CACHE.invalidate_all();
+    TAG_LIST_CACHE.invalidate_all();
+    SINGLE_POST_CACHE.invalidate_all();
+    POST_STATS_CACHE.invalidate_all();
+    TAG_POSTS_CACHE.invalidate_all();
+}

src/main.rs

@@ -1,4 +1,5 @@
 mod api;
+mod cache;
 mod auth;
 mod components;
 mod context;