refactor: drop cross-project spec-validation parser machinery

The fence-label -> parser fact, the specify/grounding-check/planner
parse gates, the parse-trace attestation, and all their cross-references
served a single real user (ailang). Convention over configuration: the
generic machinery is removed plugin-wide; the one consumer carries an
equivalent project-local directive in its own CLAUDE.md.

Archive under docs/plans and docs/specs left intact as time documents.

docs/conventions.md

@@ -112,7 +112,6 @@ Under `## Skills plugin: project facts`, where applicable:
 | **doc-build command** | docwriter | Optional; prints warnings on stderr. |
 | **regression scripts** | audit (bencher) | Optional list; non-zero exit = regress. |
 | **architect sweeps** | audit (architect) | Optional list; non-zero exit = drift suspicion. |
-| **spec-validation parsers** | specify, grounding-check | Optional; fence-label → `{ext, cmd}` table. `cmd` MUST contain `{file}`. Absent label → documented skip, never silent pass. |
 | **design ledger** | architect, most agents | Optional path (e.g. `design/INDEX.md`). |
 | **glossary** | every role | Optional path; implicitly standing reading. |
 | **design contracts / models** | docwriter, specify | Optional dirs. Aspirational-source frontmatter marker recommended (see below). |
@@ -140,5 +139,5 @@ validated-against: <commit-sha | "no validation">
 
 When the marker is absent the signal is simply absent — `specify`
 degrades to treating the content as unmarked, never hard-failing.
-Content lifted from an aspirational source is flagged and must clear
-the parse-every-block gate before it ships in a spec.
+Content lifted from an aspirational source is flagged as a target,
+not verified fact, before it ships in a spec.