Reduce TLS memory requirements for KOReader sync

Split heap gate into separate free-memory (50KB) and largest-block (20KB) thresholds based on field measurements. Enable wolfSSL single-precision ECC to use fixed 256-bit arrays instead of heap-allocated fast-math bignums, reducing TLS handshake memory footprint. Reclaim ~7KB by right-sizing ESP timer task stacks and move WiFi code out of IRAM to free ~25-30KB for heap. Add memory audit landmarks for font and EPUB allocations.

lib/Epub/Epub.h

@@ -44,6 +44,7 @@ class Epub {
   }
   ~Epub() = default;
   std::string& getBasePath() { return contentBasePath; }
+  // MEMFIX-PORT: epub resident-bytes audit accessor; portable
   // 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.

lib/Epub/Epub/Section.h

@@ -132,6 +132,7 @@ class Section {
   // (covers finalized sections and partials from a previous session).
   std::optional<uint16_t> findAnchor(const std::string& anchor) const;
 
+  // MEMFIX-PORT: section resident-bytes audit accessor; portable
   // Approximate resident heap for the audit log. Steady state (no build) a
   // Section holds little beyond itself; during a build the page LUT and path
   // strings dominate (the parser's internal footprint is not walked here).

lib/Epub/Epub/css/CssParser.h

@@ -67,6 +67,7 @@ class CssParser {
    */
   [[nodiscard]] static CssStyle parseInlineStyle(std::string_view styleValue);
 
+  // MEMFIX-PORT: stylesheet resident-bytes audit accessor; portable
   // 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.