docs(declare): document the YAML declare format

Update the journal-set doc entry, the CLI diagnostic table, and the
authoring skill, along with the in-app empty-state hint and the var
message comment.

.agents/skills/tttk-authoring/SKILL.md

@@ -60,7 +60,7 @@ Fenced blocks are dispatched by the `role=` attribute in the info string:
 |---|---|
 | ` ```csv role=spark-table ` | Body is CSV; replaced with `:md-table[./csv_<hash>]`. First column header must be a dice formula (`d6`, `2d6+1`, …). |
 | ` ```markdown role=spark-table ` | Body is a GFM pipe table; converted to CSV, then same as above. |
-| ` ```csv role=declare ` | Defines reactive variables / tag modifiers. Block is stripped. |
+| ` ```yaml role=declare ` | YAML `vars:` / `tags:` maps defining reactive variables and tag modifiers. Block is stripped. |
 | ` ```<lang> role=file ` | Body stored as text content, block stripped, referenced by its derived id. |
 | ` ```yaml role=tag ` | Kept intact; rendered as a custom element from YAML (`tag:`, `body:`, …). |
 | ` ```<lang> ` (no role) | Rendered as a normal visible code block. |
@@ -109,7 +109,7 @@ Warnings are usually real too:
 | Code | Meaning |
 |---|---|
 | `TTTK-R002` | spark-table first header is not a dice formula |
-| `TTTK-R004` | `role=declare` row skipped (empty `key` or `expr`) |
+| `TTTK-R004` | `role=declare` block declares nothing |
 | `TTTK-C002` | reference resolves to an unexpected file type |
 | `TTTK-L002` | `#section` matches no heading |
 | `TTTK-A001` | icon missing under `assets/` |