chore: fix project conventions — .gitignore, CHANGELOG categories, docs naming

Assisted-by: MiMo V2.5 Pro

README.md

@@ -225,7 +225,7 @@ Remaining for Phase 2:
 
 - External (cross-package) symbol references in the GOOBJ output —
   **deferred** with a recorded decision and three options; see
-  [`docs/DEFERRED.md`](docs/DEFERRED.md).  Single-package objects (no
+  [`docs/decisions.md`](docs/decisions.md).  Single-package objects (no
   cross-package references) work today, which covers the production
   kernels.  With that item deferred, the amd64 instruction set — scalar,
   VEX/AVX2 and the full EVEX/AVX-512 set including GPR-interchanging
@@ -322,8 +322,8 @@ portable Go implementation every kernel is derived from.
 | `cmd/gasm` | The `gasm` binary tying it all together. |
 | `_gen` | The generator that rebuilds the instruction tables from the Go toolchain. |
 
-See [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) for the design rationale and
-data flow, and [`docs/DEFERRED.md`](docs/DEFERRED.md) for design decisions
+See [`docs/architecture.md`](docs/architecture.md) for the design rationale and
+data flow, and [`docs/decisions.md`](docs/decisions.md) for design decisions
 deliberately postponed (with the analysis needed to pick them up again).
 
 ## Quick start