v1.15.0

v1.15.0 — Fleet ROI overlay + minor-bump rollup of today's hotfixes

New feature: fleet-level block ETA on the home dashboard. Aggregates
each online device's blockProbability by chain, sums the per-second
rates, inverts to days/years. Renders one tile per active chain below
the existing summary HUD — mixed BTC + BCH fleets get one rollup
each, single-chain fleets get one tile, empty fleets render nothing.

All computation is client-side using the per-device data already in
/api/devices — no extra request, no backend changes. Math:
   per_sec(fleet) = Σ per_sec(device) = (Σ GH/s × 1e9) / (2^32 × diff)
holds because share difficulty is linear in hashrate at constant
network difficulty.

Why minor-version-bump-with-feature instead of v1.14.4: today's
suppression rule fix (v1.14.3) only takes effect *after* a user
upgrades to it. Users still on v1.14.0/.1/.2 are silenced for any
v1.14.x successor. A minor bump (v1.14.x → v1.15.0) bypasses that
suppression because (1,14) ≠ (1,15) — so the banner fires correctly
for everyone, regardless of which v1.14.x they're stuck on.

APP_VERSION bump 1.14.3 → 1.15.0. PRO_FEATURES.md: Fleet ROI overlay
moved from "Ideas under consideration" to shipped.