add Dockerfile and Rocky Linux 9 build docs

Introduces a Docker-based build path so ior can be compiled on any
Linux host without a native Rocky 9 toolchain setup:

- Dockerfile: Rocky 9 minimal image with Go (version from ARG, default
  from go.mod), static libelf/libzstd built from source, libbpfgo at
  v0.9.2-libbpf-1.5.1, and mage; CMD runs mage generate + mage all
  against the repo root mounted as a volume.
- scripts/build-with-docker.sh: reads GO_VERSION from go.mod, passes it
  as --build-arg to docker build, mounts tracefs and BTF into the
  container, writes the binary to the repo root.
- Magefile.go: adds BuildDocker target that wraps the script.
- README.md: simplified to the two build paths (Docker + native) with
  links to docs/; removed GOTOOLCHAIN=auto throughout.
- docs/build-rocky-linux-9.md: full manual Rocky 9 steps, libbpfgo
  toolchain setup/rollback, compile-once-run-everywhere explanation,
  and timing semantics.
- docs/tui-reference.md: complete TUI hotkey reference, recording mode
  details, and the .ior.zst vs Parquet trade-off table.
- AGENTS.md: removed GOTOOLCHAIN=auto from all build commands.
- internal/c/generated_tracepoints.c: regenerated against the host kernel.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/Magefile.go b/Magefile.go
index cf1adfb..e9458b5 100644
--- a/Magefile.go
+++ b/Magefile.go
@@ -40,6 +40,7 @@ const (
 	tracepointsResultNew = "internal/c/generated_tracepoints_result.txt.new"
 	tracepointsGoPath    = "internal/tracepoints/generated_tracepoints.go"
 	typesGoPath          = "internal/types/generated_types.go"
+	dockerBuildScript    = "scripts/build-with-docker.sh"
 	typesHeaderPath      = "internal/c/types.h"
 	VMLINUXPath          = "internal/c/vmlinux.h"
 	benchProfilesDir     = "bench-profiles"
@@ -72,6 +73,16 @@ func All() error {
 	return nil
 }
 
+// BuildDocker builds the ior binary inside a Rocky Linux 9 Docker container
+// and writes the resulting static binary to the repo root.  The container
+// image is built on the first run (~15-20 min) and reused thereafter.
+// The Go version baked into the image is taken from go.mod automatically.
+// Requires Docker and a host kernel with tracefs and BTF enabled.
+// Pass --run to skip the image rebuild and only recompile ior.
+func BuildDocker() error {
+	return sh.RunV("bash", dockerBuildScript)
+}
+
 // BpfBuild builds the embedded BPF object used by the Go binary.
 func BpfBuild() error {
 	if err := ensureVMLINUX(); err != nil {