fix(igdb): don't match series games to their base title

[gantoine]

Description
^{Explain the changes or enhancements you are proposing with this pull request.}

Fixes #3805 (a recurrence of #3309, only partially addressed by #3400).

Series titles like Metal Gear Solid: Portable Ops Plus / Portable Ops and the Pokémon Ranger games were resolved to the same IGDB id, and therefore the same SteamGridDB id, as their base game, so distinct ROMs ended up as siblings. Hasheous and RetroAchievements (hash-based) matched them correctly; only the name-search providers were wrong.

Root cause

IGDBHandler._search_rom runs a first pass filtered by game_type (MAIN_GAME, EXPANDED_GAME, PORT, REMAKE, REMASTER, STANDALONE_EXPANSION), which excludes types like EXPANSION. So a more specific variant is frequently absent from that pass's candidates. Jaro-Winkler scores the base title against the searched variant very high for prefix/superset titles (measured with the repo's own matcher: portable ops plus vs portable ops = 0.9928; Pokémon Ranger variants ≈ 0.90–0.91), all far above the 0.75 match threshold. The base was therefore accepted and returned before the broader search passes ever ran. SteamGridDB then inherited the wrong title because fetch_sgdb_details seeds its search from the IGDB name first.

Fix

• Add _is_prefix_superset_match() to detect when one title's words are a proper prefix of the other's.
• Only trust a first-pass hit outright when it's an exact match or not a prefix/superset near-miss. Otherwise widen the search: re-query without the game_type filter (the reliable recovery, since the variant is often an excluded type) alongside the existing expanded /search pass, then re-rank across the union so an exact variant (score 1.0) outranks the base near-miss (0.99). The base stays in the candidate pool, so it remains the fallback when no better match exists.

The gate keeps this cheap: exact matches and ordinary fuzzy matches still return on the first pass with no extra API calls; only genuine prefix ambiguity triggers widening.

AI assistance disclosure

Per CONTRIBUTING.md: this change was written with AI assistance (Claude Code / Opus 4.8). The diagnosis, implementation, and tests were AI-generated and human-reviewed.

Checklist
^{Please check all that apply.}

• I've tested the changes locally
• I've updated relevant comments
• I've assigned reviewers for this PR
• I've added unit tests that cover the changes

Full metadata test suite (321 tests) passes, including 9 new tests covering the prefix heuristic and the _search_rom widening/no-widen paths. trunk check (ruff/black/isort/mypy) clean.

Screenshots (if applicable)

N/A (backend metadata-matching change)

🤖 Generated with Claude Code

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[greptile-apps]

Greptile Summary

This PR broadens IGDB matching when a first-pass result is a prefix near-match. The main changes are:

• Detect proper title-prefix relationships after normalization.
• Retry without the game-type filter for ambiguous first-pass matches.
• Re-rank candidates from all search passes together.
• Add tests for variant recovery and first-pass short-circuiting.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• Platform filters remain applied during widening.
• Existing candidates remain available as fallbacks during re-ranking.
• Focused tests cover the new matching paths.

Important Files Changed

Filename	Overview
backend/handler/metadata/igdb_handler.py	Adds prefix-aware widening and re-ranks the combined IGDB candidate set.
backend/tests/handler/metadata/test_igdb_handler.py	Covers prefix detection, excluded-type recovery, exact matches, and ordinary fuzzy matches.

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