fix(overview): mining addresses visible at 0 balance; drag-reorder always applies

- Address list: a mining-flagged address stays visible even at 0 balance when
  "hide zero balances" is on (payout addresses shouldn't vanish).
- Drag-reorder: persist dense sort orders (0..N-1) for the whole visible list on
  drop via App::reorderAddresses, instead of a pairwise swap that no-ops when both
  rows are still at the default un-ordered state. First drag now always takes
  effect, and explicit order keeps overriding the starred/type/balance sort.
- Tests: 0-balance mining row survives hide-zero; ordered non-favorite outranks a
  favorite.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -252,6 +252,10 @@ public:
     void setAddressSortOrder(const std::string& addr, int order);
     int getNextSortOrder() const;
     void swapAddressOrder(const std::string& a, const std::string& b);
+    // Assign dense sort orders (0..N-1) to the given addresses in the given order and
+    // persist once. Used by drag-reorder so a drop always takes effect (even from the
+    // default un-ordered state, where a pairwise swap would be a no-op).
+    void reorderAddresses(const std::vector<std::string>& orderedAddrs);
     bool isMiningAddress(const std::string& addr) const;
     void setMiningAddress(const std::string& addr, bool mining);
     void invalidateAddressValidationCache();