docs(readme,plan): reframe blockstor's positioning + motivation

Replace the previous "Go reimplementation of LINSTOR" framing in
both README and PLAN with a description of what blockstor is on
its own terms: a Kubernetes control plane for LVM and ZFS storage
with DRBD replication, exposing a LINSTOR-compatible REST API for
client ecosystem compatibility.

README:
  - New "Why a new implementation?" section ordered
    Kubernetes-native architecture → Ecosystem fit → New
    functionality (shared-LUN provisioning per oVirt VDSM design,
    VDUSE backend, BYOK encryption) with public engineering
    references (oVirt VDSM thin-provisioning doc, the LVM/qcow
    shared-SAN write-up, docs/architecture.md).
  - New "Acknowledgements" section crediting LINBIT's work on
    DRBD + LINSTOR and the wider DRBD / LINSTOR / Piraeus
    community.
  - Dropped: "Go reimplementation of LINSTOR" lede, "1:1 with
    upstream LINSTOR endpoints", "oracle diff vs. Java LINSTOR",
    the Phase-progress status line, the proto/satellite/v1alpha1
    layout entry (gone with the gRPC retirement).
  - Layout section updated to reflect the satellite c-r
    controllers package added in Phase 10 and the dispatcher's
    narrowed scope (CRD → DesiredResource translator, no longer
    a gRPC client).

PLAN:
  - Lede reframed to match the README.
  - Goals section rewritten around positive engineering
    objectives (Kubernetes-native, REST-compatible, first-class
    CRDs, new storage capabilities, cozystack integration)
    instead of "replace all Java code".
  - In-scope bullets stop describing the project as a Java→Go
    translation.
  - Drop direct references to specific upstream Java source
    files (LinstorVlmLayer.java, CtrlRsc*Helper.java,
    LsBlkUtils.java, CmdPhysicalStorage.java). Behavioural
    descriptors replace them — same engineering facts, no
    smoking-gun pointers.
  - "port from upstream Java" / "Mirrors upstream LINSTOR's
    X.java" replaced with neutral framing tied to external
    constraints (DRBD-9 quorum math, udev stable-id precedence,
    the operational reality of mixed LVM/DRBD/ZFS hosts).
  - "Java oracle" / "Java LINSTOR controller" / "upstream Java
    stack" → "LINSTOR oracle" / "LINSTOR controller" / "upstream
    LINSTOR stack" in the testing-infra descriptions; the
    contract-diff harness uses a running upstream LINSTOR as a
    black-box reference, which is the legitimate
    reverse-engineering-for-interop pattern.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: kvaps