Diagram generation: ref-arch-driven procedure + spec validator + KB enrichment

The diagram path now follows a documented standard procedure (lookup
the closest Oracle Architecture Center reference → confirm components
→ author absolute_layout → spec validator → render → visually verify)
and ships persistent guardrails so layout regressions can't recur.

Persistent procedure changes (apply to all users, all sessions):
- tools/diagram_spec_validator.py — geometry checks (CONTAINER_TOO_THIN,
  CONTAINER_PADDING_VIOLATION, LABEL_OVERFLOW_PARENT) run BEFORE either
  renderer (drawio + PPTX). Catches the subnet-collapse / label-overflow
  bugs that the post-render drawio validator missed.
- tools/oci_diagram_gen.py + tools/oci_pptx_diagram_gen.py — call the
  spec validator before emitting any output. Adds mysql / mysql_heatwave
  type aliases.
- tools/archcenter_pattern_lookup.py — scores against cached page
  descriptions (not just the 1-line summary), supports --queries for
  multi-fragment composition, and applies synonym expansion via
  kb/architecture-center/synonyms.yaml so "LB HA cross AD" matches
  "load balancer high availability availability domain".
- kb/architecture-center/synonyms.yaml — canonical synonym table
  (load balancer, autonomous database, data guard, …) used by the
  lookup scorer.

KB enrichment:
- tools/archcenter_description_fetcher.py + 121 cached _description.md
  under kb/diagram/assets/archcenter-refs/<slug>/. Removes the runtime
  dependency on docs.oracle.com when authoring specs and feeds the
  pattern-lookup scorer.
- 110+ cached .drawio / .svg / .png references for offline reuse,
  plus the OCI Toolkit v24.2 import (kb/diagram/assets/oci-toolkit-drawio).

Documentation:
- docs/skill/output-formats.md — new "Standard diagram-generation
  procedure (MANDATORY)" + geometry rules + the new validator entry.
- SKILL.md option 2 — references the mandatory procedure.
- README.md — describes the spec validator, archcenter_pattern_lookup
  and description fetcher, and updates the KB-health table.

Tooling that backs the procedure (cumulative across recent sessions):
tools/archcenter_case_runner.py, archcenter_batch_driver.py,
archcenter_zip_downloader.py, drawio_visual_validator.py,
drawio_fidelity_eval.py, harvest_drawio_icon.py, import_oci_library.py,
oci_pptx_diagram_gen.py, oci_pptx_render.py, refresh_pptx_icon_index.py.

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

config/output-formats.yaml

@@ -4,7 +4,7 @@
 output_selection:
   description: |
     The architect can specify output format when requesting deliverables:
-      deck              ← default, just the slide deck
+      deck              ← default, slide deck with native OCI PowerPoint diagram when applicable
       deck + drawio     ← deck + editable diagram
       deck + doc        ← deck + detailed technical document
       deck + xlsx       ← deck + detailed cost spreadsheet
@@ -22,12 +22,12 @@ output_selection:
     deck:
       extension: ".pptx"
       generator: "tools/oci_deck_gen.py"
-      description: "10-12 slide architecture proposal"
+      description: "10-12 slide architecture proposal with native OCI PowerPoint diagram when applicable"
 
     drawio:
       extension: ".drawio"
       generator: "tools/oci_diagram_gen.py"
-      description: "Editable architecture diagram (draw.io)"
+      description: "Editable architecture diagram (draw.io) for technical editing workflows"
 
     doc:
       extension: ".docx"
@@ -133,7 +133,7 @@ deck_structure:
 
     - number: 3
       type: architecture_diagram
-      content: "Full architecture diagram (85% of slide)"
+      content: "Full architecture diagram (85% of slide), preferring native OCI PowerPoint shapes over pasted images"
       style: "White background, diagram fills slide"
 
     - number: 4