fix(mining): remediate mining-tab audit (22 findings) — crash-safety, async control, validation, math

Fixes all 22 confirmed findings from the mining-tab audit (10 Medium, 12 Low; 0 Critical/High),
adversarially reviewed (6 follow-ups found + fixed, incl. the review-caught idle-auto-start bypass
and a wrong benchmark-restore condition).

Crash-safety & lifecycle:
- M-04: join a stale/finished monitor thread in XmrigManager::start() and ~XmrigManager so an xmrig
  crash-then-restart (or quit) no longer std::terminate()s the wallet.
- L-03/L-10: surface an unexpected miner exit once and clear the stale running flag.

UI never blocks (M-03/L-06/L-08/L-09/L-13): pool start/stop now run on a dedicated serialized FIFO
mining-control thread (joined before teardown), so the ~13 call sites don't block the render thread on
stop()'s SIGTERM->SIGKILL->join; the spawn result marshals back to the UI.

Miner-process / pool trust boundary:
- M-01: validate the payout address (util::isValidRecipientAddress) at EVERY start path — the UI gate
  AND App::startPoolMining() (idle auto-start / thread scaling) — so a stale/wrong-chain address can't
  silently lose rewards.
- M-09: SSRF guard skips the background pool-stats GET for loopback/private/link-local/single-label hosts.
- M-02/L-02: cap the pool-stats + xmrig-API HTTP response bodies.
- L-01: write the xmrig config 0600 at creation (POSIX open with mode) — no world/group-readable window.
- M-10: reject shell-metacharacter binary paths before the version popen (excluding '()' so Program Files
  (x86) still works).

Solo mining: M-06/M-08 clamp thread count to [1, cores] at the setgenerate/xmrig boundary; M-07 notify +
don't lie on stop failure.

Correctness: L-05 block-time constant 75->150s (chainparams); M-05 discloses pool-mode "Est. Daily" as a
rough solo-equivalent; L-04/L-11/L-12 benchmark lifecycle (cancel on nav-away / mode-switch with restore,
skip rebalance mid-benchmark); L-07 honor cancel mid-extract in both the xmrig and daemon updaters.

Two new i18n keys back-filled across all 8 languages; CJK subset font rebuilt for the new glyphs.
Verified across full-node, lite, and Windows builds; tests pass.

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

res/lang/ja.json

@@ -886,6 +886,7 @@
     "mining_difficulty_copied": "難易度をコピーしました",
     "mining_est_block": "予測ブロック",
     "mining_est_daily": "予測日収",
+    "mining_est_daily_pool_sub": "おおよそのソロ換算（プール手数料前）",
     "mining_filter_all": "すべて",
     "mining_filter_tip_all": "すべての収益を表示",
     "mining_filter_tip_pool": "プール収益のみ表示",
@@ -914,6 +915,7 @@
     "mining_open_in_explorer": "エクスプローラーで開く",
     "mining_payout_address": "支払いアドレス",
     "mining_payout_foreign": "⚠ この支払いアドレスは現在のウォレットに含まれていません — マイニング報酬が別のウォレットに送られます。ウォレットを切り替えた場合は更新してください。",
+    "mining_payout_invalid": "有効な DragonX アドレスではありません — 開始前に修正してください。さもないとマイニング報酬が失われます。",
     "mining_payout_tooltip": "マイニング報酬の受取アドレス",
     "mining_pool": "プール",
     "mining_pool_fee": "手数料",