Add memory profiling for EPUB and heap diagnostics

Adds residentBytes() and cssRuleCount() methods to track EPUB memory usage including parsed CSS. Enhances memory audit logging with EPUB heap usage, max allocatable block size, and CSS rule count. Implements one-shot heap block map dump on first settled audit to identify fragmentation and long-lived allocations.

lib/Epub/Epub.h

@@ -44,6 +44,17 @@ class Epub {
   }
   ~Epub() = default;
   std::string& getBasePath() { return contentBasePath; }
+  // Approximate resident heap of the open book (audit): path strings, the CSS
+  // file list, and the parsed stylesheet. BookMetadataCache is file-backed
+  // (counts + HalFile handles) and contributes little.
+  size_t residentBytes() const {
+    size_t total = sizeof(Epub) + tocNcxItem.capacity() + tocNavItem.capacity() + filepath.capacity() +
+                   contentBasePath.capacity() + cachePath.capacity();
+    for (const auto& f : cssFiles) total += sizeof(f) + (f.capacity() > 15 ? f.capacity() : 0);
+    if (cssParser) total += cssParser->residentBytes();
+    return total;
+  }
+  size_t cssRuleCount() const { return cssParser ? cssParser->ruleCount() : 0; }
   bool load(bool buildIfMissing = true, bool skipLoadingCss = false);
   bool clearCache() const;
   void setupCacheDir() const;

lib/Epub/Epub/css/CssParser.h

@@ -67,6 +67,19 @@ class CssParser {
    */
   [[nodiscard]] static CssStyle parseInlineStyle(std::string_view styleValue);
 
+  // Approximate resident heap of the parsed stylesheet, for the audit log.
+  // unordered_map cost model: bucket array + one node per rule (libstdc++ node
+  // overhead ~= 2 pointers + hash) + key string capacity when it exceeds SSO.
+  size_t residentBytes() const {
+    size_t total = rulesBySelector_.bucket_count() * sizeof(void*);
+    for (const auto& kv : rulesBySelector_) {
+      total += sizeof(void*) * 2 + sizeof(size_t);  // node overhead
+      total += sizeof(kv);
+      if (kv.first.capacity() > 15) total += kv.first.capacity();  // beyond SSO
+    }
+    return total;
+  }
+
   /**
    * Check if any rules have been loaded
    */