docs: replace pre-2.0 landing-page illustration with editable SVG

The hero image on the docs landing page was a 1 MB raster bundling a
diagram and a code snippet; the editable source had been lost. The
snippet used pre-2.0 type names (longblob, double).

Replace with a hand-written SVG (5 KB) that:
- depicts a calcium-imaging pipeline using the vocabulary already in
  calcium-pipeline.svg and computation-model.md
- follows DataJoint's notation: rectangles for Manual/Lookup, ovals
  for Imported/Computed, encoded by both shape and color
- uses 2.0 type syntax (int32, <blob@>) and the canonical make() form
- preserves the original zoom-in callout from the highlighted node
  to its definition, with the same pedagogical annotations
- uses the lighter pastel palette already in calcium-pipeline.svg

The SVG is its own source — committed as text, no separate editable
asset to lose.

Author: dimitri-yatsenko

src/images/pipeline.png

@@ -9,7 +9,7 @@
 
 **DataJoint** implements the [Relational Workflow Model](explanation/relational-workflow-model.md)—a data model where your database schema defines an executable data pipeline. Tables represent workflow steps, foreign keys encode dependencies, and the system handles job management, parallel execution, and provenance tracking. [Object storage](explanation/data-pipelines.md#object-augmented-schemas) integration enables seamless handling of large scientific data.
 
-![pipeline](images/pipeline.png){: style="height:300px;"}
+![pipeline](images/pipeline.svg){: style="width:100%;max-width:1100px;"}
 
 <div class="grid cards" markdown>