chore: prepare release v0.31.0

CHANGELOG.md

@@ -11,6 +11,18 @@ Unreleased changes on the `development` branch.
 
 ### Added
 
+-
+
+## [0.31.0] — 2026-08-20
+
+The arm64 encoder (Phase 5 — complete) ships with ELF64 and GOOBJ emission,
+verified byte-for-byte against `GOARCH=arm64 go tool asm` and linked into a
+real `go build`.  The encoder covers the full integer instruction set, FP
+arithmetic, conditional select, CRC32, and the MOV pseudo-instruction with
+bitmask immediate encoding.  The project now requires Go 1.27.
+
+### Added
+
 - **arm64 encoder (Phase 5 — complete).**  `gasm asm` can now assemble `_arm64.s`
   files: the AArch64 integer instruction set with the MOV pseudo-instruction and
   its immediate-constant expansions (MOVZ/MOVN/MOVK for wide immediates, ORR with
@@ -22,6 +34,12 @@ Unreleased changes on the `development` branch.
   verification against `GOARCH=arm64 go tool asm` matches byte-for-byte.  Phase 5
   (the other architectures — RISC-V, LoongArch, arm64) is now complete.
 
+### Changed
+
+- **Go 1.27 required.**  The project now requires Go 1.27 (`toolchain go1.27.0`).
+  The `R_DWTXTADDR_U4` relocation type is detected at runtime for backward
+  compatibility.
+
 ## [0.30.0] — 2026-08-13
 
 The LoongArch encoder (Phase 5) ships with ELF64 and GOOBJ emission, verified