docs: address Copilot review round 6 on #2203

The truncation guard rejected valid frontmatter. It assumed the only way
a raw scalar can exceed its parsed value is a comment, but YAML also
strips presentation syntax, so `description: &copy Some text` and
`description: !!str Some text` were both reported as truncated — naming
an unquoted `#` the value does not contain.

The length check is now gated on an actual comment marker: `#` at the
start of the scalar or preceded by whitespace, which is where YAML begins
a comment. Anchors and tags fall out before the length is consulted.
Regression cases cover both, and assert the genuine `#` case still fails
so the fix cannot pass by disarming the guard.

Also corrects the checklist, which still said an unquoted `#` lets every
check pass. That predated the verifier; verify:skills rejects it now, and
the sentence was telling authors the gate is blind to something it
catches.

No skill description or eval case changed, so skills:eval is unchanged
from round 4's 63/63. local:gate passes, 34/34. 391/391 script tests.

Signed-off-by: cliffhall <cliff@futurescale.com>

docs/skill-authoring.md

@@ -234,7 +234,10 @@ break.
    description containing `:` or `#` is **quoted**. An unquoted colon loads the
    body with an _empty_ description, so `/name` still works while the skill can
    never auto-fire again; an unquoted `#` is worse-behaved, truncating the
-   description from that point on so it stays non-empty and every check passes.
+   description from that point on so it stays *non-empty* — which is why it went
+   unnoticed until `board-ops` lost both its board numbers. `verify:skills` now
+   rejects that truncation, so the gate catches it; quote the value rather than
+   relying on the check to tell you.
 2. `disable-model-invocation` is declared explicitly; default it to `false`.
 3. Description is action-first, with `Use when …; when …; when …`.
 4. **If the skill is model-invoked**, `evals/evals.json` carries **at least