Add changeset; re-sync the two docs pages tied to this bug

CLAUDE.md requires a docs re-sync when a promoted skill's behaviour
changes, and a changeset for versioning. Full re-syncs of all ten
touched skills' docs pages would be disproportionate for a wording-only
change to internal invocation instructions, but two pages specifically
document the exact reliability problem this phrasing targets — the
"most reported problem" FAQ on grill-with-docs's page, and the matching
"rough edge" FAQ on grilling's page, plus a stale literal quote of
grill-me's SKILL.md body. Updated those three spots to reflect the new
mechanism without overclaiming the bug is fully fixed, and added a
changeset summarizing the change across all ten affected skills.

Co-Authored-By: Claude <noreply@anthropic.com>

.changeset/skill-tool-invocation-terminology.md

@@ -0,0 +1,9 @@
+---
+"mattpocock-skills": patch
+---
+
+Standardize cross-skill invocation on an explicit "call the Skill tool" instruction instead of bare `/skill`-style prose, across `code-review`, `diagnosing-bugs`, `grill-with-docs`, `grill-me`, `improve-codebase-architecture`, `tdd`, `to-spec`, `to-tickets`, `triage`, and `wayfinder`.
+
+- A skill that names another skill in prose ("run the `/grilling` skill") does not reliably cause it to load — this is the documented rough edge behind `grill-with-docs`'s most-reported problem. Naming the tool directly (`Call the Skill tool with "grilling"`) is intended to raise the hit rate. Dropping the leading `/` also makes the instruction harness-neutral rather than less: it no longer assumes Claude Code's trigger syntax.
+- A step needing more than one skill now says so as multiple calls ("Call the Skill tool twice, for `grilling` and `domain-modeling`"), not one call carrying two names.
+- Documents the convention in `.agents/invocation.md` for future skills to follow.