hygiene: Phase 6 (partial) — fix 7 verified bugs + quick-wins + dedup

From the Phase-6 structural scoping: land the verified behavioral bugs and
the safe quick-wins/dedups now; the large refactors (monolith splits, ~180
header globals) and consensus-adjacent items stay deferred. Built clean;
self-mined; verifychain=true.

BUGS (verified by reading the code):
- net.cpp CNode::Ban: a braceless `if (subNet.Match(...))` left
  `pnode->fDisconnect = true;` OUTSIDE the guard, so banning any one subnet
  marked EVERY connected peer for disconnect (dropped the whole peer set).
  Wrapped the two statements in braces. (LIVE, high severity.)
- rpcdump.cpp importwallet: the `!fGood -> throw "Error adding some keys"`
  check was trapped inside the `if (fRescan)` block, so importwallet with
  rescan=false silently reported success when key import failed. Hoisted the
  check before the rescan branch and cleaned the garbled braces/indentation.
- wallet.cpp CommitTransaction: ignored AddToWallet()'s return, so a failed
  disk-persist of a just-signed spend was swallowed while the tx broadcast.
  Now logs a hard error on failure.
- hush_nSPV_fullnode.h: the UTXOS branch declared `uint8_t filter` while the
  twin TXIDS branch uses `uint32_t filter`; dragon_rwnum switches on
  sizeof(filter), so the utxos path parsed only 1 of 4 wire filter bytes.
  Widened to uint32_t.
- asyncrpcoperation_sweep.cpp: LogPrintf("%s ... %s", one-arg) read a missing
  vararg; added the __func__ argument.
- rpcdump.cpp importprivkey: inner `auto secret_key` shadowed the outer
  uint8_t and changed the type into DecodeCustomSecret; dropped the shadow.
- rpcdump.cpp getrescaninfo: char[8] + sprintf("%.4f") overflows when the
  ratio >= 10.0 (transient reorg); widened to char[16] + snprintf.

QUICK WINS: removed the duplicate DRAGON_MAXSCRIPTSIZE #define; pinned the
dead HUSH3-branch NOTARISATION_SCAN_LIMIT_BLOCKS to 1440; fixed init typos
(fRequestShutdown, RPC warmup).

DEDUP: extracted the 19-line try/catch error-mapping block — copy-pasted
identically into all six async operations — into
AsyncRPCOperation::set_error_from_current_exception(), so the mapping is
edited in one place. Behavior-identical (verified all six blocks were byte-
identical first).

Deferred (endorsed by the scoping, better as their own PRs): addrman Select_
dedup, the pow.cpp powLimit helper (consensus file), the miner CreateNewBlock
lock-asymmetry, the wallet monolith splits, and the ~180-global / consensus-
retarget / Komodo-heritage work.

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

src/wallet/asyncrpcoperation_shieldcoinbase.cpp

@@ -116,23 +116,8 @@ void AsyncRPCOperation_shieldcoinbase::main() {
 
     try {
         success = main_impl();
-    } catch (const UniValue& objError) {
-        int code = find_value(objError, "code").get_int();
-        std::string message = find_value(objError, "message").get_str();
-        set_error_code(code);
-        set_error_message(message);
-    } catch (const runtime_error& e) {
-        set_error_code(-1);
-        set_error_message("runtime error: " + string(e.what()));
-    } catch (const logic_error& e) {
-        set_error_code(-1);
-        set_error_message("logic error: " + string(e.what()));
-    } catch (const exception& e) {
-        set_error_code(-1);
-        set_error_message("general exception: " + string(e.what()));
     } catch (...) {
-        set_error_code(-2);
-        set_error_message("unknown error");
+        set_error_from_current_exception();
     }
 
 #ifdef ENABLE_MINING