fix(scanners): hide swag in Door Check and sessions in Swag Pickup

[JacobCoffee]

Summary

• Door Check was showing T-Shirt categories and Swag Pickup was showing Tutorials / Sponsor Presentations / Summits — both pages call `/check_in/redeemable/` which returns the union of every redeemable category and `CategorySerializer` only emits `(id, name)`, so the client had nothing to discriminate on.
• Filter the response client-side by category name in each page's `ngOnInit`:
  • Door Check keeps categories not matching `/shirt|swag/i`.
  • Swag Pickup keeps categories matching `/shirt|swag/i`.
• Products are also filtered to those whose surviving category is in the kept set, so "All sessions in this category" + the search list don't leak through.

A comment in each `ngOnInit` points at the proper long-term fix (expose `render_type` on `CategorySerializer` in `pycon-site` and filter on `render_type === 10` for presentations).

Effect — given `pycon-site/fixtures/inventory.json`

Page	Categories shown after fix
Door Check	Tutorials, Sponsor Presentations, Job Fair Add-On, Summits and Events, PyLadies Auction
Swag Pickup	Conference T-Shirts, Charlas T-Shirts, PyLadies T-Shirts

Test plan

• `make serve`, sign in as someone with check-in permissions.
• Open Door Check: chips contain only sessions/events (no shirts). Pick Tutorials → product list is tutorial sessions only.
• Open Swag Pickup: chips contain only T-Shirt categories. Pick Conference T-Shirts → product list is shirt sizes only.
• Scan a real attendee QR on each page; redemption flow still works (server-side `?mode=…` filter is unchanged).

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