docs: proofread awf-config-spec for W3C-style conformance

Rewrite the AWF Configuration Specification to follow W3C-style
conventions consistently throughout:

- Add Abstract section summarizing document purpose and audience
- Restructure Status of This Document to distinguish normative from
  informative content
- Expand §1 Conformance with full RFC 2119 keyword list, hyperlinked
  reference, and definitions for conforming document and conforming
  implementation
- Rewrite §2 Processing Model in formal imperative style with ordered
  steps and cross-references
- Rewrite §3 Precedence Rules using SHALL with highest-wins ordering
  and informative note
- Expand §4 Data Model with a proper table of top-level properties
- Normalize §5 CLI Mapping formatting: consistent use of config-only
  annotations and CLI-only callout
- Rewrite §6 and §7 in formal W3C language
- Restructure §8 Environment Merge Semantics with tables instead of
  bullet lists, blockquoted notes, and consistent RFC 2119 usage
- Restructure §9 Credential Isolation Semantics with subsection
  headers matching config values and formal SHALL/MUST/MAY usage
- Add Normative References and Informative References sections

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lpcox