fix: remap card template index using source note id on apkg import

[krMaynard]

Linked issue (required)

Fixes #5209

Summary / motivation (required)

import_cards remapped a card's template index (ord) inside add_card, which runs after map_to_imported_note has already overwritten card.note_id with the target note id. But notetype_map — and therefore remapped_templates — is keyed by the source note id, so the lookup missed and the template index was left unchanged whenever a note's id changed on import (id-collision uniquify, or a guid match to a differently-id'd note).

Consequences: cards could point at the wrong template after import, and card_ordinal_already_exists deduplicated on the un-remapped ordinal.

The fix computes the remapped index in import_cards using the source note id, before map_to_imported_note runs, via a small pure helper.

Steps to reproduce (required, use N/A if not applicable)

1. Have a collection whose notetype template ordinals were reordered relative to a source deck.
2. Export a deck to .apkg where an imported note's id collides with an existing note (forcing uniquify) or matches by guid to a differently-id'd note.
3. Import the .apkg into the target collection.
4. Observe that affected cards render with the wrong template (their ordinal was not remapped).

How to test (required)

Checklist (minimum)

• I ran ./ninja check or an equivalent relevant check locally (via the fork CI run linked below).
• I added or updated tests when the change is non-trivial or behavior changed.

Details

Adds a unit test for the remap lookup exercising the source-note-id keying. Full CI (check on Linux/macOS/Windows, format, minilints) was run against this exact commit on the fork: https://github.com/krMaynard/anki-fork/actions/runs/30167008557 — build, lint, and test pass on all three OSes. (The run shows red only for the Upload SARIF results for complexipy step, which always fails on forks due to a token-permission limitation, not a code failure.)

Before / after behavior (optional)

Before: template ordinals silently left un-remapped when a note's id changed on import. After: ordinals remapped using the source note id.

Risk / compatibility / migration (optional)

Low risk; import-path-only change, no schema or scheduling impact.

UI evidence (required for visual changes; otherwise N/A)

N/A

Scope

• This PR is focused on one change (no unrelated edits).