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/README.md

@@ -10,7 +10,7 @@ Publishes tech blog posts from `mikkeli/tech-blogs` to `https://wiki.novoyuuparo
 - YAML frontmatter parsing per [SCHEMA.md](SCHEMA.md)
 - Pandoc-based markdown → wikitext body rendering (h1 elements preserved)
 - Auto-generated banner (`{{Auto-generated|source=...|commit=<sha>}}`)
-- Category injection: `[[Category:Tech blog]]` on every page; `[[Category:Blog:<year>]]` from `date` field; `[[Category:<tag>]]` per tag entry
+- Category injection: `[[Category:Tech blog]]` on every page; `[[Category:Blog:<year>]]` from `date` field (falling back to the action's execution year); `[[Category:<tag>]]` per tag entry
 - No title prefix — pages live at their bare title
 - MediaWiki bot API write with idempotency — no-op if wiki content matches generated output
 - Files without `wiki.publish: true` silently skipped
@@ -65,7 +65,7 @@ Shared code lives in `lib/wiki.py` (repo root).
 |---|---|---|
 | No title prefix | Tech posts live at bare titles — no namespace needed | 2026-06-10 |
 | Fixed category | Every post gets `Category:Tech blog` | 2026-06-10 |
-| Year category | `Category:Blog:<year>` from `date` field; omitted if no date | 2026-06-10 |
+| Year category | `Category:Blog:<year>` from `date` field; falls back to the execution year if no date | 2026-06-10 |
 | Tag categories | Each tag → `[[Category:<tag>]]` with no prefix | 2026-06-10 |
 | WIP exclusion | None — `wiki.publish: false` is the only gate | 2026-06-10 |
 | Publish mode | Always `--all` | 2026-06-10 |