Reflect M0 landing in docs

Retarget README to ReaSampler and current build targets; reconcile
CLAUDE.md repo-identity + targets table to reaper_reasampler; archive
Milestone 0 from PLAN.md into new COMPLETED.md.

PLAN.md

@@ -14,35 +14,6 @@ it here and appends it to `COMPLETED.md`.
 
 ---
 
-## Milestone 0 — Transition scaffold: reaper_mpeview → ReaSampler
-**Goal:** Retire the MPE scaffold and stand up the sampler's pure core in its
-place, preserving the pure-core / REAPER-shell split.
-**Verify:** `cmake -B build -S .` configures clean; `cmake --build build` builds
-the renamed extension target and the pure-core test target; `ctest --test-dir
-build` is green with the new `bank_model` + `peaks` suites present.
-
-- [ ] Delete `src/mpe_model.{h,cpp}` and `src/mpe_view.{h,cpp}`; remove
-  `tests/test_mpe_model.cpp`.
-- [ ] Rename the CMake `project()` and the extension MODULE target from
-  `reaper_mpeview` to `reaper_reasampler` (binary `OUTPUT_NAME` likewise);
-  update `PREFIX ""` / platform SUFFIX blocks to the new target name.
-- [ ] Replace the pure `mpe_model` static lib + `mpe_model_tests` executable with
-  `bank_model` (pure static lib) + `bank_model_tests`; keep the CTest wiring.
-- [ ] Repoint `src/main.cpp`: drop the `mpe_view.h` include and all `MpeView_*`
-  calls (toggle / IsOpen / OnTimer / Cleanup); stub the extension entry so it
-  loads, logs to console, and registers nothing MPE-specific. The
-  `command_id` / `gaccel` / `hookcommand` registration *pattern* is preserved for
-  reuse (CLAUDE.md §REAPER extension contract) — the MPE action string is removed.
-- [ ] Choose and record the persistent action-id prefix for the sampler family
-  (replaces `CEREBELLUM_MPEVIEW_TOGGLE`); this string is forever-stable once
-  shipped (CLAUDE.md §action registration).
-- [ ] Refresh `README.md` layout/next-step sections to the sampler module set.
-  (Landed-work reflection is doc-keeper's; this point exists so the stale MPE
-  README does not mislead the first implementer.)
-
-> After Milestone 0, Milestones 1 and 2 below are the pure-core heart. They are
-> also the near-term slice tracked in `TODO.md`.
-
 ## Milestone 1 — bank_model + JSON round-trip (pure)
 **Goal:** The `Sample` metadata struct and `BankIndex` (add / remove / query /
 tier moves / dedup-by-hash) with JSON serialize/deserialize to `std::string`.