_scan_deliverables in src/projio/mcp/questio

_scan_deliverables in src/projio/mcp/questio.py:1018 doesn't know about presentio decks.

Current behavior: the scanner walks docs/deliverables/{reports,presentations,posters}/ and for presentation/poster subdirs looks for slides.md / poster.md / index.md as the "primary file." Presentio decks use deck.yml (YAML manifest, not markdown) as their primary artifact, with sections/*.md underneath. The scanner either skips presentio decks (no primary .md found) or picks an arbitrary section file's frontmatter via the md_files[0] fallback at line 1059 — either way the deliverables overview page will be wrong for presentio decks.

Fix: teach _scan_deliverables to recognize deck.yml in presentation subdirs. When deck.yml is present, parse it as YAML and construct the fm-like dict with title from spec.title, type="presentation", format from spec.format, date from spec (if present) or dir mtime. Fall back to the current primary-file logic if no deck.yml (keeps back-compat with the old slides.md convention).

Context: this is a latent bug introduced by the presentio path migration to docs/deliverables/presentations/ (2026-04-19). The projio-intro deck at docs/deliverables/presentations/projio-intro/ is the first real test case — it'll be missing or mis-indexed in the deliverables overview until this lands.

Related: docs/specs/quarto-reports.md §6 introduces report_build; that tool will have a similar concern for .qmd-based reports vs. the current .md-only report scanning. Worth fixing both in one pass.