chore: migrate to Aspect CLI AXL tasks on ephemeral GHA runners

[gregmagolan]

Migrate CI from Aspect Workflows (.aspect/workflows/config.yaml) to the Aspect CLI on ephemeral GitHub Actions runners.

Adds

• .aspect/version.axl — pins the Aspect CLI to 2026.21.44.
• .aspect/config.axl — opts in to artifact uploads (testlogs/profile/BEP), sets --config=ci in CI, registers an aspect buildifier alias of aspect format.
• .github/workflows/ci-workflows.yaml — matrix test job on (workspace × Bazel 8/9; Bazel 9 excluded from examples/uv_pip_compile) plus single buildifier and gazelle jobs.
• tools/format/BUILD.bazel — format_multirun(name = "buildifier") (Starlark-only).
• tools/gazelle/BUILD.bazel — aspect_gazelle(languages = ["starlark"]) from aspect_gazelle_prebuilt.
• Root //:gazelle and //:buildifier aliases into tools/.
• README note linking to the Aspect CLI docs / install.
• rules_go 0.60.0 and rules_nodejs 6.7.4 pinned as dev_deps — aspect_rules_lint's transitive versions reference legacy global symbols (CcInfo, incompatible_use_toolchain_transition) removed in Bazel 9.

Removes / renames

• .aspect/workflows/config.yaml and .aspect/workflows/bazelrc — bazelrc settings hoisted into root .bazelrc under :ci with --lockfile_mode=off (lock is gitignored).
• Inline root aspect_gazelle() and buildifier() rules (moved into tools/).

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Changes are visible to end-users: no

Test plan

• CI on this PR

[aspect-workflows]

✨ Aspect Workflows Tasks

📅 Mon May 25 01:56:53 UTC 2026

✅ 7 successful tasks

• ✅ buildifier · ⏱ 29.3s · 🐙 GitHub Actions · ☑️ Check
  💬 Format complete (clean)
• ✅ gazelle · ⏱ 28.3s · 🐙 GitHub Actions · ☑️ Check
  💬 Gazelle complete (clean)
• ✅ test (test-e2e-bazel-8) · ⏱ 30m 27s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (137/137 passed)
• ✅ test (test-e2e-bazel-9) · ⏱ 3m 6s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (132/132 passed · 127 cached)
• ✅ test (test-examples-uv_pip_compile-bazel-8) · ⏱ 23.8s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-root-bazel-8) · ⏱ 2m 52s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (184/184 passed · 184 cached)
• ✅ test (test-root-bazel-9) · ⏱ 2m 24s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (183/183 passed · 183 cached)

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