feat(release): add linux/s390x and linux/mipsle to goreleaser builds (#1265)

Add s390x and mipsle (softfloat) architecture targets to all three
goreleaser build entries (picoclaw, picoclaw-launcher, picoclaw-launcher-tui).

Go only supports these architectures on Linux, so no additional
ignore entries are needed — goreleaser skips unsupported OS/arch
combinations automatically.

mipsle uses GOMIPS=softfloat for maximum compatibility with
FPU-less MIPS cores (e.g. MT7620 with MIPS 24KEc).

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.goreleaser.yaml

@@ -32,9 +32,13 @@ builds:
       - riscv64
       - loong64
       - arm
+      - s390x
+      - mipsle
     goarm:
       - "6"
       - "7"
+    gomips:
+      - softfloat
     main: ./cmd/picoclaw
     ignore:
       - goos: windows
@@ -59,9 +63,13 @@ builds:
       - riscv64
       - loong64
       - arm
+      - s390x
+      - mipsle
     goarm:
       - "6"
       - "7"
+    gomips:
+      - softfloat
     main: ./cmd/picoclaw-launcher
     ignore:
       - goos: windows
@@ -86,9 +94,13 @@ builds:
       - riscv64
       - loong64
       - arm
+      - s390x
+      - mipsle
     goarm:
       - "6"
       - "7"
+    gomips:
+      - softfloat
     main: ./cmd/picoclaw-launcher-tui
     ignore:
       - goos: windows