feat(anki): import a deck built in Anki to seed known words (#228)

[HugoFara]

Implements what #228 actually asks for, following this review.

The gap this closes

#228's body: "Many users have anki decks with thousands of words, it would be much faster than reclassifying whether each word is known."

The .apkg support in #259 does not provide that, despite sharing the file format — it round-trips LWT's own exports, matching notes by lwt- guid. I verified the gap rather than assuming it, by building a stock Anki "Basic" deck and running it through ApkgReader:

ApkgReader returned: 3 notes
  lwtTermId=0  term=''  translation=''  suspended=no   (x3)
Notes ApkgImportService would skip as 'no LWT id': 3 of 3

Three notes read, three skipped, nothing changed. This PR adds the missing direction.

How it works

Two steps, because an .apkg records neither a language nor which field means what:

1. Upload — LWT lists the note types in the file with their field names and note counts.
2. Map — pick the note type, the term field, an optional translation field, the language, and how status should be decided.

Status is derived from Anki's own scheduling, which is what makes this faster than reclassifying:

In Anki	Becomes
Suspended	98 — Ignored
Never studied	1
1–6 days	2
7–13 days	3
14–20 days	4
21+ days	99 — Well known

The 21-day line is Anki's own mature card threshold, the same one its statistics screen uses, so it matches what users already believe about their deck. A fixed-status mode is available when that doesn't fit.

A note with several cards is judged by its strongest card, and only counts as suspended when every card is — otherwise forward/reverse pairs would under-report knowledge.

Details worth reviewing

• AnkiFieldText reduces Anki's HTML fields to plain text — tags stripped, <br> and block ends to spaces, entities decoded, [sound:…] removed, {{c1::…}} cloze answers kept. Without it markup lands in the reading view and terms never match words in a text.
• Create-only. Re-importing the same deck is safe; duplicates within one file collapse case-insensitively.
• The parked upload is keyed by a session entry, not a request parameter, so step 2 can't be pointed at an arbitrary path on disk.

Also fixed

The round-trip importer reported foreign notes as "Skipped (no LWT id)" — which reads like a bug to someone importing their own deck. It now says the notes weren't created by LWT, and both the page and the docs link to the new importer. The docs page for the old feature gained a warning up top, since arriving at the wrong one is the obvious wrong turn.

Verification

44 new tests: reader coverage for arbitrary field names, scheduling extraction, negative (sub-day) intervals and tags; status mapping pinned at every boundary; table-driven HTML cleaning including non-Latin scripts; and integration tests running the whole path against real MySQL — derived statuses, re-import safety, in-file duplicate collapsing, HTML stripping, optional translation, tag import.

psalm 0 errors, phpcs PSR12 clean, typecheck clean, 9143 tests green, integration suite 165.

Not in scope

Live sync — split out to #264 with the reasoning: AnkiConnect binds to 127.0.0.1 so a server can't reach it, AnkiWeb has no public API, and bidirectional sync is the Phase 4 conflict-resolution problem.