feat(explorer): fuzzy search — filter the block list by partial hash/height

Add a fuzzy mode to the explorer search: a non-numeric, non-full-hash query now
filters the list to cached blocks whose hash (or height text) contains the query
substring, live as you type. Backed by a new ExplorerBlockCache::searchBlocks()
(SQLite LIKE with escaped wildcards), memoized per query so it doesn't hit the DB
every frame. Exact queries still navigate precisely: a block height re-anchors
the list, and a full 64-char hash is resolved via RPC. Row clicks still open the
detail modal. Empty results show "No matching cached blocks".

Note: fuzzy matching covers cached (browsed/prefetched) blocks only — the daemon
has no partial-hash index — while exact height/hash lookups reach any block.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/explorer/explorer_block_cache.h

@@ -3,6 +3,7 @@
 #include <cstdint>
 #include <map>
 #include <string>
+#include <vector>
 
 struct sqlite3;
 
@@ -41,6 +42,9 @@ public:
     const std::string& databasePath() const { return database_path_; }
 
     std::map<int, ExplorerBlockSummary> loadRange(int minHeight, int maxHeight);
+    // Fuzzy search over cached blocks: matches when the query is a substring of the height (as text)
+    // or the block hash (case-insensitive). Returns newest-first, capped at `limit`.
+    std::vector<ExplorerBlockSummary> searchBlocks(const std::string& query, int limit);
     bool storeBlock(const ExplorerBlockSummary& block);
     int cachedBlockCount();
     void clearBlocks();