[NRT-591] Surface duplicate anki_id suggestion error + redesign bulk suggestion summary

[RisingOrange]

Related issues

• Closes NRT-591 (add-on side)
• Depends on backend NRT-783 / AnkiHubSoftware/ankihub#3702 for the conflicting-id error payload — degrades gracefully without it, so the two can ship independently.

Proposed changes

When a user submits a new-note suggestion for a note whose anki_id already exists in the deck on AnkiHub (note created + auto-accepted, then edited and re-suggested before a sync), the server rejects it with "A deck can't contain multiple notes with the same anki_id.". Previously this failure was effectively hidden (single → raw showInfo; bulk → an uncategorized blob in the plain-text summary). This PR surfaces it and lets the user recover.

Detection (main/suggestions.py)

• ANKIHUB_DUPLICATE_ANKI_ID_ERROR constant + parse_duplicate_anki_id_error() — tolerates the backend's DRF-normalized payload (list-wrapped/stringified: reads conflicting_ankihub_id[0], compares conflicting_note_deleted[0] == "True", not truthiness).
• Resubmit core: _new_note_to_change_suggestion() converts the already-built NewNoteSuggestion into a ChangeNoteSuggestion keyed by the conflicting ah_nid and lets the server diff — no remote fetch, no AnkiHub-DB write. resubmit_new_note_as_change_suggestion() (single) and resubmit_new_notes_as_change_suggestions_in_bulk() (one batched call).
• suggest_notes_in_bulk now returns already_in_deck_by_nid on the result; soft-deleted conflicts are routed to the existing deleted-on-AnkiHub category instead (a change suggestion would 404 a tombstoned note).

Scenario 1 — single suggestion (gui/suggestion_dialog.py)

• New NoteAlreadyExistsDialog (info icon, Cancel / Send as change suggestion). The suggestion dialog closes and the modal shows over the editor; on success → toast; soft-deleted conflict → existing "deleted from AnkiHub" dialog; missing conflicting id (older server) → falls back to today's generic error.

Scenario 2 — bulk suggestion summary (gui/suggestion_dialog.py)

• Replaces the plain-text showText summary with a real BulkSuggestionSummaryDialog, shown for all outcomes (full redesign): colored counts, bold (N) category titles, a new "Other errors" bucket with a community.ankihub.net/c/support link, and the redundant "All notes with failed suggestions" block removed.
• New interactive "Notes already in this deck" action box: Resubmit (one batched create_suggestions_in_bulk call) / Ignore; Close/X disabled until resolved; "Updated" badges on changed categories; a hard resubmit failure re-enables Close (no dead-end).

Analytics (structlog → Datadog): error_dialog_shown, resubmit_clicked, bulk_error_category_shown, bulk_resubmit_clicked.

How to reproduce

As a maintainer on staging:

1. Create a new note in Anki using one of your deck's AnkiHub note types and Suggest it (auto-accepts so the note is created on AnkiHub).
2. Don't sync. Edit the same note and suggest it again.
3. Before: the failure was hidden (single: a raw error; bulk: an uncategorized failure count).
4. After: single → "Note already exists in this deck" dialog with Send as change suggestion; bulk → the note lands in the "Notes already in this deck" action box with a Resubmit as change suggestions button.

Tests: pytest tests/addon -k "BulkSuggestionSummaryDialog or MaybeHandleNoteAlreadyExists or ParseDuplicate or NewNoteToChange or OnSuggestNotesInBulkDone or already_in_deck".

Screenshots and videos

All dialog states (single modal, bulk default / loading / success / ignored) were verified live against the real add-on code. Design reference: the Figma + mockups on NRT-591. (Can add inline screenshots on request.)

Further comments

• Resubmit avoids any local AnkiHub-DB write — it converts the failed new-note suggestion directly, so there's no half-synced state; trade-off is that editing the same note again before a sync could re-trigger the error (a normal sync reconciles it).
• Root-cause "persist the generated ankihub_id on accept" was deliberately rejected — it would couple the add-on to synchronous server-side note creation, which may change; dedup belongs server-side.
• Open design question (not blocking): per-category note IDs currently render as truncated lists (first 25, … and N more). A "Copy note IDs" button (copying an Anki Browse nid:… search) is proposed and pending designer confirmation.
• Built as a separate branch off main, not stacked on the auto-protect flag cleanup ([NRT-771] Post-flag-flip cleanup: drop AUTO_PROTECT_FEATURE_FLAG scaffolding + thread NoteDiff #1305) which touches the same two files; the overlap is mechanical, not architectural.