chore(changeset): record the Vale rule engine at the bottom of the stack

`require-changeset` only ever evaluates the bottom PR's own diff, so a changeset
written on the tip is invisible to the PR that actually merges — removing
`skip-changeset` from this PR turned the check red with the note sitting three
branches above it.

The stack merges down, so nothing lands until everything does and one note
describing the whole change is accurate at the only moment it is read. It is
moved here rather than duplicated; the tip's copy goes away as the units restack
onto this commit.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jwc9FFroR3mTZ4hLiSkkX3

Author: thecodedrift

.changeset/vale-rule-engine.md

@@ -0,0 +1,17 @@
+---
+"@taskless/cli": minor
+---
+
+Add Vale as a second static-tier rule engine.
+
+`check` now dispatches by engine directory and runs ast-grep, Vale, and runtime
+rules concurrently, merging their findings into one result set. Vale rules live
+in `.taskless/vale/` and execute against the committed `.vale.ini`; an
+unavailable Vale reports itself and the other engines still return, while a Vale
+that times out or rejects its config fails the check rather than passing as a
+clean run. Vale rules are verified from `rule-tests/<rule>/pass|fail` fixtures
+against a generated per-rule config.
+
+Adds the `engine-selection` knowledge topic — which engine enforces a given
+rule, and why — available from `taskless help engine-selection` and exported
+through `@taskless/cli/prompts`.