chore: rename docs/specs/SPEC.md and faces.md to .adoc #96

Background

The estate documentation-format rule (DOC-FORMAT in .claude/CLAUDE.md) is:

All documentation files in docs/ must use .adoc extension.
Exception: GitHub community-health files must use .md by name (CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, CHANGELOG.md, README.md).

Two files in docs/specs/ on main predate this rule and still use .md. Neither matches the community-health exception.

Files to rename

• docs/specs/SPEC.md → docs/specs/SPEC.adoc
• docs/specs/faces.md → docs/specs/faces.adoc

What "rename" means here

For each file:

1. git mv docs/specs/<name>.md docs/specs/<name>.adoc
2. Convert Markdown syntax to AsciiDoc:
   • Headings: #/##/###/#### → =/==/===/====
   • Pipe-tables → [cols="..."] |=== blocks
   • Fenced code (```lang) → [source,lang] `----` listings
   • Emphasis: **bold** → *bold*, *italic* → _italic_
   • Inline code (`x`) stays the same
3. Add the standard preamble at top:

   // SPDX-License-Identifier: PMPL-1.0-or-later
   = <Title>
   :toc: macro
   :toclevels: 2
   :source-highlighter: rouge
   
   toc::[]
   

4. Grep the rest of the repo for inbound references to the old .md paths and update each one (e.g. docs/specs/SPEC.md referenced from other specs, READMEs, justfiles, CI scripts, the bin/main.ml --help blurb if applicable).

Acceptance

• Both files renamed and rewritten in valid AsciiDoc.
• git grep -nE 'docs/specs/(SPEC|faces)\.md' returns no hits except in CHANGELOG-style historical notes.
• The PR body lists every inbound reference touched.

Why this is good-first-issue

The conversion is mechanical, the rule is documented in .claude/CLAUDE.md (DOC-FORMAT), and docs/specs/affex-spec.adoc (landed on PR #93's branch) is a worked example of the same Markdown → AsciiDoc conversion at this scale.

Out of scope

• Do not touch any open PR's branch as part of this work — SPEC.md and faces.md show up in several open PRs' diffs and renaming them mid-PR creates merge churn. Wait for those PRs to merge or be closed, then do this rename in a single small PR against main.