docs: record Phase 1 NO-GO + Phase 2 pivot to ZRAWDATA via libdivecomputer

Phase 1 spike concluded (see docs/import-formats/macdive-zsamples.md
on feature/macdive-zsamples-phase-1). ZSAMPLES decoding ruled out —
probably block-cipher encrypted; not crackable in the timebox.

Pivot: decode ZRAWDATA via the already-integrated libdivecomputer_plugin.
Shearwater dives have 100% co-coverage of ZRAWDATA/ZSAMPLES (267/267);
pivot gives 49% of all dives (76% of dives with any sample data) via a
certain, maintained code path.

This commit:
- Appends Phase 1 outcome + pivot rationale to the profile-decoding
  design spec.
- Adds continuation pointers at the tail of the parent MacDive SQLite
  plan.
- Adds the Phase 2 implementation plan for the ZRAWDATA pivot, gated
  on a pre-work investigation of the libdivecomputer_plugin API.

Author: ericgriffin

docs/superpowers/plans/2026-04-21-macdive-sqlite-import.md

@@ -1953,3 +1953,12 @@ git commit -am "chore: changelog for MacDive SQLite import"
 - Core Data's NSDate epoch is 2001-01-01 00:00:00 **UTC**. Don't localize.
 - If you see warnings about `ZRAWDATA` or `ZSAMPLES` being non-null but empty: MacDive writes a placeholder bplist for dives without profile data. Treat as empty and carry on.
 - ZRAWDATA/ZSAMPLES BLOB decoding → sample profile population is intentionally punted to a follow-up. Opening it in this milestone risks making the PR too large; the mapper has a clear integration point to receive decoded profile arrays later.
+
+## Continuation
+
+Follow-up work closing the "profile samples" gap:
+
+- **Design spec:** `docs/superpowers/specs/2026-04-23-macdive-sqlite-profile-decoding-design.md`
+- **Phase 1 spike plan (completed):** `docs/superpowers/plans/2026-04-23-macdive-zsamples-phase-1-spike.md`
+- **Phase 1 outcome:** NO-GO on `ZSAMPLES` (proprietary format, probably block-cipher encrypted). Full findings at `docs/import-formats/macdive-zsamples.md`.
+- **Phase 2 plan (pivot):** `docs/superpowers/plans/2026-04-23-macdive-profile-phase-2-zrawdata.md` — decodes `ZRAWDATA` via the existing `libdivecomputer_plugin` for 100% coverage of Shearwater dives (267/267).