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/util/i18n.cpp

@@ -1364,6 +1364,7 @@ void I18n::loadBuiltinEnglish()
         strings_["explorer_tx_outputs"] = "Outputs";
         strings_["explorer_tx_size"] = "Size";
         strings_["explorer_invalid_query"] = "Enter a block height or 64-character hash";
+        strings_["explorer_no_results"] = "No matching cached blocks";
 }
 
 const char* I18n::translate(const char* key) const