test(lint): back the Vale 3.15.2 behaviour claims with a committed test

The `house-vale-3-15-2-repro` provenance entry claimed behaviours were
reproduced against purpose-built fixtures, but no fixtures existed, so
the earlier commit in this PR removed it. Commit the fixtures.

tests/test-vale-3-15-2-behaviours.sh builds its fixtures in a temp dir
and runs the real Vale. It exits 77 (skipped) when vale is missing or is
not 3.15.2. It asserts the six vale-config behaviours and the vale-run
ones (unmapped .mdx, `vale off` variants, the spelling ignore file, and
the ls-* commands never naming a rule).

Restore the entry in both sources.md files as `Research doc: none` with
`Basis:` naming the test, and re-add its source_keys. Two behaviours are
not asserted: the native-MDX suppression column (needs mdx2vast) and the
`vale sync` row that adds to Packages (needs the network). The wording in
configuration-reference.md and troubleshooting.md now says so.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EGHFJextYtVQseaHPDDhxB

plugins/lint/.apm/skills/vale-config/references/configuration-reference.md

@@ -2,6 +2,7 @@
 topic: configuration-reference
 source_keys:
   - context7-websites-vale-sh
+  - house-vale-3-15-2-repro
 ---
 
 ## Core Settings
@@ -81,7 +82,7 @@ Only *package* styles need fetching. A style whose YAML rule files are already c
 - `Vale.Avoid` — enforces the project's rejected vocabulary terms.
 - `Vale.Repetition` — flags repeated words (e.g. "the the").
 
-`Packages` (top-level, what `vale sync` downloads) and `BasedOnStyles` (per-glob, what activates) are separate keys: a style lints a file only once it is in both. Every row below reproduced against Vale 3.15.2:
+`Packages` (top-level, what `vale sync` downloads) and `BasedOnStyles` (per-glob, what activates) are separate keys: a style lints a file only once it is in both. Every row below is asserted against Vale 3.15.2 by `tests/test-vale-3-15-2-behaviours.sh` (slug `house-vale-3-15-2-repro`) except the `vale sync` row that adds the name to `Packages`, which needs the network and is not covered:
 
 | Configuration | Result |
 |---|---|
@@ -97,7 +98,7 @@ Only *package* styles need fetching. A style whose YAML rule files are already c
 
 ## Frontmatter Scopes
 
-House-verified behaviour, not documented on vale.sh — reproduced locally against Vale 3.15.2.
+House-verified behaviour, not documented on vale.sh — asserted against Vale 3.15.2 by `tests/test-vale-3-15-2-behaviours.sh` (slug `house-vale-3-15-2-repro`).
 
 A rule scoped to `text.frontmatter.<key>` (e.g. `text.frontmatter.description`) matches reliably when that field's value is a single physical line, and breaks on most — not all — multi-line forms. Multi-line forms spanning 2+ lines: