Show4DSTEM: accept inspection products (DPC_r/DPC_c/SSB phase) as map presets

[bobleesj]

Why

Collaborators often already have BF/ADF/DPC/SSB products from a prior run. They should open one Show4DSTEM widget and switch between raw 4D navigation and those maps without re-running SSB inside the widget.

Show4DSTEM(
    data,
    products={
        "DPC r": dpc_r,
        "DPC c": dpc_c,
        "SSB": ssb.phase,   # phase only; amplitude not required for v1
    },
)

The widget shows those as selectable map presets/tabs. Do not run SSB (or other heavy recon) inside Show4DSTEM by default.

Scope

Show4DSTEM (this issue — implement first)

• Add products= (or equivalent) argument.
• Accept 2D arrays and simple 3D stacks (e.g. multi-frame products).
• Register names in the map selector / preset row with same label font as existing BF/ABF/ADF controls.
• Use a sensible colormap scheme:
  • DPC r / DPC c: diverging (e.g. coolwarm / RdBu-style), zero-centered when appropriate
  • SSB phase: cyclic or standard phase map consistent with house style (match existing SSB/phase displays if any)
• If a value looks like an SSBResult-like object, auto-register phase only (not amplitude) for v1.
• No heavy SSB compute inside Show4DSTEM unless explicitly requested later.

Out of scope for this issue (follow-ups)

• ShowPtycho: rich ptycho/SSB exploration (aberrations, defocus sweep, loss, metadata) — separate track / GH ShowPtycho: offline HTML + folder export (kernel-less share, WebGPU play) #186 offline path.
• Bridge: “open in ShowPtycho” / pass crop/frame/scan coords from Show4DSTEM — later.
• Amplitude product — not needed for v1 (Bob: people care about phase + DPC r/c).

Design split

Surface	Role
Show4DSTEM	4D navigation + passed-in inspection products (DPC r/c, SSB phase)
ShowPtycho	Full SSB/ptycho interactive exploration

Acceptance

• products={"DPC r": ..., "DPC c": ..., "SSB": ...} works on Show4DSTEM
• Map selector lists product names next to / with BF/ADF-style presets
• Switching product updates the virtual-image panel without kernel SSB
• Colormaps: DPC diverging; SSB phase appropriate; label font matches existing presets
• Docs or docstring example with post-SSB embed into Show4DSTEM
• Unit test: register 2D products, switch selection, bytes shape match scan

Refs

• Second-brain: Show4DSTEM inspection products
• Related: ShowPtycho offline/WebGPU GH ShowPtycho: offline HTML + folder export (kernel-less share, WebGPU play) #186 (do not merge concerns)