fix(events): match listing duplicates by headliner and venue identity - #3966

Closes #3965

Problem

The mosplaceradio.com/bandschedules listings import (flow 983, job 1986789) created 341 events and matched 0 existing ones. The AI step sends a venue name plus city/state with no street address, titles like Headliner with Support at Venue, and loose venue names. Two gaps:

1. Venue resolution (Venue_Taxonomy::resolve_venue_identity): Iron Horse Music Hall vs The Iron Horse, Paradise Rock Club vs Paradise Rock Club presented by Citizens, Roadrunner vs Roadrunner-Boston, John F. Swope Theater, Capitol Center for the Arts vs Capitol Center for the Arts. The exact, article and normalized tiers miss these, and the core-name tier needs exact core equality. Result: about 100 new venue terms.
2. Event dedup (EventDuplicateStrategy): even on the same venue term, the fuzzy title check compares full titles (fantastic cat at iron horse music hall vs fantastic cat at iron horse 2 shows, hunxho vs hunxho 2night only tour), so the result was CLEAR.

Fix

• Venue_Taxonomy: new venue_variant_key() and venue_names_are_variants(), built on core_venue_name(). They strip "presented/powered/sponsored/hosted by …", a trailing parenthetical, a "-" suffix, a trailing "music hall", and a standalone "at", and also accept a multi-word prefix or a Room, Venue comma part. resolve_core_name_tier() accepts these variants only when the incoming venue has no street address and has a city. It still requires has_positive_location_evidence(). More than one compatible term returns ambiguous (no term is created). A match reports matched_via = name_variant.
• EventDuplicateStrategy: new Strategy 2b, findByHeadlinerAndVenueIdentity(). It compares headlinerKey() (strips " at " or a venue variant, support/co-bill lists, tour or ":" subtitles, and accents; keeps "Late Show" / "Night 2" set names) for same-day candidates at the same venue term or at a same-city name-variant term. Time window: the normal window, or the strict one-hour window for low-confidence keys. Outside the window, a single cross-source candidate is accepted (mirrors Strategy 2), except for low-confidence keys at a variant venue.

Prod evidence (read-only simulation over the 82 already-trashed duplicates from this import)

• Before: 4/82 detected. After: 56/82 detected.
• On 289 surviving events from the same import: 4 new hits, all genuine duplicates. One of them, Tusk at the Academy of Music, has since been trashed manually.
• Venue scan: re-resolving all 110 import-created venue terms with those terms hidden gives 15 name_variant matches, 0 ambiguous, and none across cities. Examples: Roadrunner → Roadrunner-Boston, The Sinclair → The Sinclair Music Hall, The Drake → The Drake - Amherst, Brighton Music Hall → … presented by Citizens. Two are room- or stage-level merges, allowed by the prefix rule: Off the Rails (Worcester) → Off The Rails Outdoors, and Arts at the Armory Cafe → Arts at the Armory.
• Deliberately unmatched: Angela Autumn at Rockwell (Boston) vs Rockwell - MA (Somerville), because the cities differ.

Tests

• tests/Unit/EventDuplicateHeadlinerVenueTest.php: Hunxho/Big Night Live tour suffix (same time and cross-source), Whitechapel support list, Iron Horse variant venue, Béla Fleck accents with a room-qualified venue, Street Dogs sponsor variant. Negatives: different headliners at different venues, same headliner at two different same-city venues, Open Mic at X vs Open Mic at Y, same headliner in a different city, one-word headliner at a variant venue outside the window. Plus headlinerKey() cases.
• tests/Unit/VenueTaxonomyListingVariantTest.php: Iron Horse Music Hall + Northampton, MA resolves to The Iron Horse (name_variant). Variant data provider. Two-term ambiguous case. Other-city, no-city and street-address negatives. Single-word-prefix negative.

Left out

• Accented venue term fixtures in PHPUnit: the WP Codebox SQLite test DB returns no get_terms() rows once such a term exists. Accent folding is covered via headlinerKey() tests and was verified on prod MySQL (e.g. Esme Hotel Rooftop Music Hall → Esmé Hotel Rooftop).
• Venue keys shorter than 5 chars (Ciné) are never treated as variants (existing FUZZY_NAME_MIN_LENGTH).
• Venues whose names share no variant relation (Wilbur Theatre vs Hava Nightclub, Off the Rails Worcester vs Off The Rails Boston, House of Blues - Boston vs Citizens House of Blues Boston, sponsor prefixes) stay unmatched on purpose.
• Merging the existing duplicate venue terms and events on prod is a separate data-cleanup job.

Written by Extra Chill Bot (AI agent) on behalf of Chris Huber.