fix(mining): make "Est. Daily" honest about variance and fees

The mining "Est. Daily" was a solo expected-value (your hashrate share x
blocks/day x a fixed block reward) rendered in the same green as the real
Today / Yesterday / All-Time earnings, off an instantaneous hashrate and
gross of pool fees. It read like a dependable daily income when it is a
long-run statistical average with huge (Poisson) variance.

Framing:
- The estimate is now drawn in a neutral colour, not the green "money
  earned" colour (the actual mined totals stay green).
- A sub-label in BOTH modes marks it as an average ("avg", or "avg, net"
  in pool mode when the fee is applied), replacing the pool-only
  "before pool fee" note.
- A hover tooltip over the column explains the variance ("often nothing
  for long stretches, then a lump - NOT a steady daily income") and the
  fee status (after the N% fee / before the fee when unknown / nothing for
  solo and 0%-fee pools).

Accuracy:
- Uses a trailing-average hashrate instead of the instantaneous / 10s
  snapshot: pool prefers hashrate_15m (then 60s, then 10s); solo uses the
  mean of hashrate_history once there are >=10 samples, else the instant
  rate. This stops a spike or a momentary dip from swinging the figure.
- Subtracts the known pool fee so pool-mode figures are net; synthetic or
  unmatched pools stay gross and the tooltip says the fee is unknown.

The static block reward and true pool-reported earnings are intentionally
out of scope (the latter needs a new pool-API field). New i18n keys are
translated into all eight locales; the CJK subset font is rebuilt for the
three new glyphs. Builds + test suites pass on both variants.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -2184,6 +2184,11 @@ void I18n::loadBuiltinEnglish()
         strings_["mining_difficulty_copied"] = "Difficulty copied";
         strings_["mining_est_block"] = "Est. Block";
         strings_["mining_est_daily"] = "Est. Daily";
+        strings_["mining_est_daily_sub"] = "avg";
+        strings_["mining_est_daily_sub_net"] = "avg, net";
+        strings_["tt_mining_est_daily"] = "A long-run statistical average for your current hashrate share of the network. Real mining rewards arrive at random (Poisson) - often nothing for long stretches, then a lump - so this is NOT a steady daily income.";
+        strings_["tt_mining_est_daily_fee_fmt"] = "Shown after the %.1f%% pool fee.";
+        strings_["tt_mining_est_daily_nofee"] = "Shown before the pool fee (fee unknown for this pool).";
         strings_["mining_filter_all"] = "All";
         strings_["mining_filter_tip_all"] = "Show all earnings";
         strings_["mining_filter_tip_pool"] = "Show pool earnings only";