Triage seed knowledge and document admission test for preview

Remove seven knowledge files whose content is generic software-engineering
guidance that a capable LLM already applies without BCQuality present
(HTTPS-only, secret-leakage-in-errors, no-credentials-in-URLs, silent
security-error swallowing, short transaction scope, HTTP timeouts,
StrSubstNo-vs-concatenation). These fail the remedial-knowledge premise
and dilute the signal of the preview corpus.

Strip the "Seed article — domain stewards should expand" banner from ten
files that are ready to showcase (AA0232/AA0233 rules, FindSet read-only
semantics, SetLoadFields ordering and usage, CalcFields-in-loops,
SecretText end-to-end, DataClassification). The banner remains on files
that still need domain-steward refinement.

Add a "What belongs here" section to the README stating the admission
test: a file exists only if a modern LLM would get something wrong or
miss something without it. Gives contributors a concrete yes/no filter
before they open a PR.

microsoft/knowledge/performance/use-setloadfields-for-partial-records.md

@@ -9,8 +9,6 @@ application-area: [all]
 
 # Use SetLoadFields for partial records
 
-> **Seed article.** Converted from an existing performance-review prompt to bootstrap the BCQuality performance corpus. Domain stewards should expand, restructure, and refine as needed.
-
 ## Description
 
 SetLoadFields instructs the platform to hydrate only the listed fields on a record variable. On wide tables, or tables with BLOB or media fields, the difference is substantial: a Sales Invoice Line has dozens of fields and loading all of them for every row of a large set is wasted bandwidth. Primary key fields, SystemId, and system audit fields are always loaded automatically. SetLoadFields works only with FieldClass = Normal; FlowFields and FlowFilters cannot be partial-loaded.