Archive Milestone 2 in docs

Move completed M2 (peaks module) from PLAN.md to COMPLETED.md; add peaks_tests
to the CLAUDE.md targets table and update the pure-core status to M0-M2 done.

PLAN.md

@@ -14,20 +14,6 @@ it here and appends it to `COMPLETED.md`.
 
 ---
 
-## Milestone 2 — peaks (pure)
-**Goal:** Compute waveform min/max bins from raw PCM, dependency-free (not
-REAPER's peak API). CONTEXT.md §Module architecture, §Non-goals.
-**Verify:** CTest green. Fed a known signal (full-scale sine, ramp), asserted
-min/max envelope per bin matches expected within tolerance; channel count
-preserved; bin count honored for arbitrary sample lengths (incl. remainder bin).
-
-- [ ] Min/max bin computation from interleaved PCM given a target bin count.
-- [ ] Multi-channel handling (per-channel envelope; no silent fold).
-- [ ] Tests: sine envelope ≈ ±amplitude; ramp envelope monotonic; DC/silence →
-  zero envelope; short-buffer and non-divisible-length edge cases.
-
----
-
 ## Milestone 3 — Offline capture spike (REAPER shell)
 **Goal:** Offline-render the time-selection master mix to a wav in the project
 bank folder, add a `Sample`, log it. The render-driving spike. CONTEXT.md