v5.9.0 — Brand kits on the tool surface

Contract refresh for API v5.226.0.

• upload_asset gains purpose=brand (forward spelling of theme — one path, two names, theme still accepted) for uploading a brand kit template.
• browse_catalog gains type=brands — list your kits with versions (theme_id=<slug> default, <slug>@<n> pins one).
• manage_account gains action=brand_report (per-token fidelity report) and action=feedback_list (read your filed reports back).
• README, llms-install.md, AGENTS.md and the skills now document brand kits.
• Fixed a real pricing error in the pdf-to-pptx skill (extraction has always billed $0.01/page, not free) and its stale claim about scanned PDFs.

Additive only — no tools or parameters removed or renamed. Full CHANGELOG entry: CHANGELOG.md.