fix(tech): default Blog year category to execution year

Dateless posts silently lost their Blog:<year> category. build_wikitext
now falls back to datetime.now().year when no date is declared, so every
published post lands in a year category. Docs corrected accordingly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pipelines/tech/SCHEMA.md

@@ -45,7 +45,7 @@ wiki:
 
 #### `date` (ISO 8601 date)
 
-Publication date in `YYYY-MM-DD` format. Drives `[[Category:Blog:<year>]]` injection. If omitted, no year category is added.
+Publication date in `YYYY-MM-DD` format. Drives `[[Category:Blog:<year>]]` injection. If omitted, the year falls back to the time the publish action runs.
 
 #### `tags` (list of strings)
 
@@ -69,7 +69,7 @@ For each `.md` with `wiki.publish: true`:
 1. Parse and validate frontmatter.
 2. Pipe the body through `pandoc -f markdown -t mediawiki`.
 4. Prepend the auto-generated banner: `{{Auto-generated|source=<source URL>|commit=<sha>}}`.
-5. Append category tags: `[[Category:Tech blog]]`; `[[Category:Blog:<year>]]` if `date` is set; `[[Category:<tag>]]` for each tag.
+5. Append category tags: `[[Category:Tech blog]]`; `[[Category:Blog:<year>]]` (from `date`, or the action's execution year if `date` is absent); `[[Category:<tag>]]` for each tag.
 6. Read the current wiki page content; if identical, skip the write (idempotency).
 7. If the page exists without `{{Auto-generated`, skip with a warning (manual page protection).
 8. Otherwise, write with an edit summary referencing the source commit.
@@ -80,7 +80,7 @@ For each `.md` with `wiki.publish: true`:
 - Pandoc-based markdown → wikitext rendering (h1 elements preserved)
 - Banner template injection
 - `Category:Tech blog` on every published page
-- `Category:Blog:<year>` from `date` field
+- `Category:Blog:<year>` from `date` field, falling back to the execution year
 - `Category:<tag>` per entry in `tags`
 - Idempotent writes
 - Manual-page protection