[TheGreatAxios]

Part of CL-12110: the approval-package deck casts from the Findings document (approval-package-preview.tsx theme, slides and blocks cast after only an isRecord check). Stacked on #167.

The hub builds each deck with slidedeck's validateDeck, but the preview read it through its own hand-written interfaces. This change makes the preview use the same definition.

Changes

• @corbits/slidedeck gains a ./deck subpath export (the schema file imports only arktype), and apps/web depends on it. A production build of the web app contains none of the PDF or PPTX writers.
• The preview validates bundle.deck with validateDeck and renders from slidedeck's types. The local deck interfaces, isRecord, the casts and branches the schema rules out are removed.
• A deck that fails validation shows the existing "could not be read" line in the Slides tab and the PDF page area, instead of drawing partial slides. The PDF download and the Sources tab keep working from the bundle, since the hub's general write path checks a deck only as an object.
• The drawing code moved to approval-package-slides.tsx, the only module that imports the deck schema, and loads with React.lazy behind a "Loading slides…" line. Building the schema costs about 150 ms (measured in Bun), so only pages that show slides pay it. In a production build the schema's strings appear only in the slides chunk.
• Nested lists are numbered like their parent unless they say otherwise, matching the PPTX and PDF writers.
• Approval rounds show "could not be read" for an unparseable bundle; the now-unused noSlides wording is removed. Validation is memoised.
• Comparison column headings are now always drawn, because the schema requires them.
• ApprovalPackageBundle.deck in packages/schemas stays Record<string, unknown>: the hub parses it on every write and stored-package read, so tightening it there would change hub behaviour.

Verification

• New tests: a deck with a partial theme shows the unreadable line with no slide text in Slides and PDF, while the download and Sources still work; a free slide draws text inside groups, and nested lists follow their parent's numbering.
• Not changed: the schema's link check uses URL.canParse, which sets a browser floor (Safari 17, Chrome 120, Firefox 115).
• Test decks that had no theme or theme.fonts were given a full theme, since the schema requires one.
• bun run lint, format:check, typecheck, test, pins:verify and vendor:verify pass.

[linear-code]

CL-12110

[corbits-triage]

Triage: Pass

No changes needed from you. A maintainer will review this pull request.

Stacked on #167: only this pull request's own changes were checked.

Notes:

• changes sensitive paths: locks: bun.lock

[corbits-triage]

No defects reported.