Improve rendering: barycentric interpolation, Gaussian blur, white-cloud palette

Replace nearest-neighbour BFS flood fill with Delaunay triangulation
(spade) + barycentric interpolation for smooth cloud boundaries.
Add NaN-aware separable Gaussian blur (σ=8 px, rayon-parallelised) to
remove triangulation facets. Switch colour scheme from blue bands to a
continuous green-to-white opacity blend matching the DWD app style.
Pixel interpolation loop is also parallelised with rayon.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.lock

@@ -8,6 +8,12 @@ version = "2.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
+
 [[package]]
 name = "android_system_properties"
 version = "0.1.5"
@@ -230,7 +236,9 @@ dependencies = [
  "clap",
  "font8x8",
  "plotters",
+ "rayon",
  "reqwest",
+ "spade",
 ]
 
 [[package]]
@@ -260,6 +268,31 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9dd111b7b7f7d55b72c0a6ae361660ee5853c9af73f70c3c2ef6858b950e2e51"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.8.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
+
 [[package]]
 name = "displaydoc"
 version = "0.2.5"
@@ -271,6 +304,18 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "either"
+version = "1.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
+
+[[package]]
+name = "equivalent"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
+
 [[package]]
 name = "fdeflate"
 version = "0.3.7"
@@ -296,6 +341,12 @@ dependencies = [
  "miniz_oxide",
 ]
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "font8x8"
 version = "0.2.7"
@@ -387,6 +438,17 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash",
+]
+
 [[package]]
 name = "heck"
 version = "0.5.0"
@@ -941,6 +1003,26 @@ dependencies = [
  "getrandom 0.3.4",
 ]
 
+[[package]]
+name = "rayon"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368f01d005bf8fd9b1206fb6fa653e6c4a81ceb1466406b81792d87c5677a58f"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22e18b0f0062d30d4230b2e85ff77fdfe4326feb054b9783a3460d8435c8ab91"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "reqwest"
 version = "0.12.28"
@@ -995,6 +1077,12 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "robust"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e27ee8bb91ca0adcf0ecb116293afa12d393f9c2b9b9cd54d33e8078fe19839"
+
 [[package]]
 name = "rustc-hash"
 version = "2.1.1"
@@ -1137,6 +1225,18 @@ dependencies = [
  "windows-sys 0.60.2",
 ]
 
+[[package]]
+name = "spade"
+version = "2.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fb313e1c8afee5b5647e00ee0fe6855e3d529eb863a0fdae1d60006c4d1e9990"
+dependencies = [
+ "hashbrown",
+ "num-traits",
+ "robust",
+ "smallvec",
+]
+
 [[package]]
 name = "stable_deref_trait"
 version = "1.2.1"