wallet: show fee-only change-only self-transfers

[kiwidream]

Summary

Closes #147.

Fee-bearing self-transfers disappeared from default wallet history when every wallet-owned output was classified as change. This PR:

• emits a transaction-level Payment to self GUI row showing the net fee debit without a misleading output index;
• emits one fee-only send entry from gettransaction, listtransactions, and default listsinceblock output, with amount: 0, the negative fee, and no synthetic address, label, or vout;
• preserves the existing detailed send/receive output behavior when include_change=true;
• adds spendable and watch-only regression coverage plus focused Qt decomposition tests.

Testing

• Built locally.
• Ran focused unit or functional tests for the changed area.
• Ran lint or formatting checks relevant to this change.
• Not run. Reason: N/A; all relevant checks above were run.

Commands/checks:

• cmake --build build --target test_bitcoin-qt qbitd qbit-cli -j8
• ctest --test-dir build -R '^test_qbit-qt$' --output-on-failure
• build/test/functional/test_runner.py wallet_listsinceblock.py --jobs=1
• cmake --build build --target rpcdocs -j8
• Docker lint suite from ci/lint_imagefile

Target Branch

• This PR targets main or a maintainer-requested release branch such as 0.1.x.

This PR targets the requested 1.x.x maintenance branch.

Risk / Review Notes

• Consensus, script, crypto, wallet, P2P, release, CI, or security-sensitive behavior changed.
• No consensus, script, crypto, wallet, P2P, release, CI, or security-sensitive behavior changed.

Notes: Wallet history presentation and RPC serialization change. Transaction construction, signing, coin selection, UTXO accounting, and balance calculation are unchanged.

Docs / Process Impact

Choose exactly one:

• I updated public docs because this PR changes user-visible behavior, integration guidance, release/process guidance, or expected validation.
• No public docs update needed. Reason:

RPC help now documents the fee-only entry and the optional output-level fields.

libbitcoinpqc Subtree Checklist (if src/libbitcoinpqc changed)

Not applicable; src/libbitcoinpqc is unchanged.

• Source commit is reachable from an immutable release tag in Qbit-Org/qbit-libbitcoinpqc.
• qbit imports the tagged upstream tree directly without pruning or a curated subtree branch.
• Subtree import/update was performed with contrib/devtools/update-libbitcoinpqc-subtree.sh.
• test/lint/libbitcoinpqc-subtree-check.sh passes locally.
• Any default tag change in contrib/devtools/update-libbitcoinpqc-subtree.sh is intentional and matches doc/subtrees/libbitcoinpqc.md.

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