docs(svg): fix architecture diagram layout bugs

Two overlap bugs in the previous architecture SVG:

* The "stamp-gated spawn" label for the hooks → consolidate gold
  arrow sat directly on top of the `errors/ · validation/` box,
  rendering both unreadable. Cause: the autonomous-loop arrow was
  routed horizontally across the same y-band as the shared/errors
  row.
* The pink "hooks imports core/infra" arrows shot vertically through
  the wiki curation subsystem callout, crossing every line of its
  text.

Layout redesign:

* Canvas grown to 780×620 to give the loop row its own band below
  the shared/errors row instead of sharing y-space.
* Wiki curation subsystem moved DOWN to a centered band under the
  core/infra row (was pinned to the bottom-left corner of core/).
* shared/ and errors/validation/ pulled together as a centered pair
  on their own row, with arrows from core/ and infrastructure/
  coming straight down.
* hooks/ + consolidate_background placed on a dedicated row at the
  very bottom of the diagram; the gold dashed arrow now runs across
  EMPTY horizontal space between them with the "stamp-gated spawn
  (TTL = 6h)" label clearly above it.
* Pink "imports core / imports infra" arrows curved out and around
  the left + right edges of the canvas (Quadratic Bézier paths)
  so they never cross the wiki subsystem callout.
* Rotated text labels on the curved pink arrows for legibility.
* Footer dependency rule kept as four-line summary.

XML parse verified.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: cdeust