docs(changelog): split [0.2.0] from pre-pivot history (closes #253)

[trilamsr]

Summary

Splits CHANGELOG.md's [0.2.0] section so it reads top-to-bottom as a coherent v0.2.0 release note (RFC-0013 pivot, OCB build, module/ submodule, OTel v0.130, otelcol_* self-tel rename, ko image, in-repo patterndetectorprocessor + rankjoinprocessor + nccl_hang + xid_correlation, recipes, helm appVersion sync, bench-check re-baseline, --version git-describe; one Removed row per delete wave PR-F.1 / PR-F.2 / PR-K.2 instead of per-package). All pre-pivot M1-M11 add-rows, internal/* add-rows, and pre-pivot fixes move to a new backdated [0.1.0-m1] - 2026-05-14 section (date derived from git log -1 --format='%cI' v0.1.0-m1). Each migrated row carries a parenthetical pointer back to the v0.2.0 PR that deleted or moved it so the cross-link is explicit. [Unreleased] is untouched. No backfilled rows for v0.1.0-m9-alpha (never tagged) per #253 out-of-scope. Closes #253.

Test plan

• bash scripts/doc-check.sh — green (493 markdown links resolve; integration-recipe gates all pass; banned-phrase + comment-noise clean)
• make check — green (fmt + tidy-check + golangci-lint + vet + go mod verify clean; the pre-commit hook also runs this)
• Manual top-to-bottom readability pass on the new [0.2.0] and [0.1.0-m1] sections
• git diff --stat: 75 insertions, 119 deletions (152 → 108 lines)
• Reviewer top-down sanity: [0.2.0] Added reads as net-new v0.2.0 surface; [0.2.0] Removed describes deletes; [0.1.0-m1] describes code that was deleted by the v0.2.0 Removed rows, with explicit forward pointers.

docs(changelog): split [0.2.0] into a v0.2.0-net-user-visible release note and a backdated [0.1.0-m1] - 2026-05-14 section for pre-pivot M1-M11 history. [Unreleased] untouched. No code changes. Closes #253.