feat(sports): promote the nine universal methods into the base classes

Phase B1b of docs/SPORTS_UNIFICATION.md. Every method here is present in
all nine bundled plugin sports.py copies and absent from core, so this is
reuse of code the fleet already agreed on — not new behavior. The
promotions are inert until B5: the plugins' own overrides still run.

SportsCore: cleanup, _get_layout_offset, _load_custom_font_from_element_config
SportsUpcoming: _select_games_for_display
SportsRecent: _get_zero_clock_duration, _clear_zero_clock_tracking,
              _select_recent_games_for_display
SportsLive: _is_game_really_over, _detect_stale_games

Where the copies disagreed, the canonical form was chosen on evidence and
the genuine per-sport differences became seams rather than branches:

- _favorite_key(game, side) -- NRL matches favorites on team id because its
  abbreviations are ambiguous (NEW is both Newcastle Knights and New
  Zealand Warriors). Default is the abbreviation; NRL overrides. Core never
  learns the string nrl.
- FINAL_PERIOD / CLOCK_COUNTS_DOWN -- hockey ends in P3, and soccer/afl/nrl
  clocks count UP, so 0:00 means kickoff, not expiry.
- _config_schema_path() / _font_root() -- plugin-supplied locations, never
  derived from this module's __file__.

BEHAVIOR CHANGE (baseball, ufc): the rejected variant coerced a missing or
non-str clock to the literal 0:00 and then declared the game over at
period >= 4. MLB has no game clock and period is the inning, so live games
were being evicted from the 5th inning onward; UFC likewise. The promoted
variant skips the clock check when the clock is unusable -- it fails safe
(keeps showing the game) instead of failing destructive.

Also fixes a regression from the package move in e591cec: the bodies were
byte-identical but __file__ gained a directory, so _resolve_project_path's
parents[2] silently began resolving to <root>/src instead of the repo root.
Both it and _font_root now derive from a single _INSTALL_ROOT constant, so
a future move needs one line changed rather than two hand-counted depths.
Tests assert the resolved values, not the index.

The font loader takes baseball's body (BDF memo cache + native-strike
retry) under hockey's Optional signature -- the older lineage is the
correct one here, and basketball's positional str default breaks on an
explicit None. It resolves through _font_root rather than the cwd, so it
does not reintroduce the bug just fixed for FontManager, and delegates to
FontManager for the alias table and BDF header parse instead of shipping
second copies. cleanup gained the two new font caches and still leaves
background_service alone -- it is a process-wide singleton.

Verified: 111 new tests (48 core + 59 modes + 4 install-root regression);
characterization + skin suites still exactly 94, unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FgbA8SMutQQpXkMG8LMmC4

docs/SPORTS_UNIFICATION.md

@@ -95,6 +95,29 @@ deprecation cycle.
 | `_custom_scorebug_layout(game, draw)` | Per-sport overlay on the base layout | no-op |
 | `render_skin_card(game, size)` | Skin-system entry point | built-in fallback |
 | `score_phrase(game)` | Celebration wording (`"GOAL"` vs `"TOUCHDOWN"`) | `"SCORE"` — only consulted when `CelebrationMixin` is present |
+| `_favorite_key(game, side)` | Which view-model field identifies a team for favorites matching | `game["<side>_abbr"]` |
+| `_config_schema_path()` | Plugin's `config_schema.json` — returning it routes `_get_layout_offset` through the `src.element_style` resolver (and gives it the defaults to compare against) | `None`, i.e. the classic inline `customization.layout` read |
+| `_font_root()` | Directory to resolve `assets/fonts` against | core install root |
+
+Two class attributes serve the same purpose for values that are per-sport
+constants rather than behavior:
+
+| Attribute | Meaning | Default |
+|---|---|---|
+| `FINAL_PERIOD` | Period at/after which a zero clock can mean "over" | `4` (hockey overrides to `3`) |
+| `CLOCK_COUNTS_DOWN` | Whether `0:00` means "expired" | `True` (soccer/afl/nrl override to `False` — their clocks count up, so `0:00` is kickoff) |
+
+### Why these are seams and not branches
+
+`_favorite_key` exists because NRL abbreviations are **not unique** — "NEW" is both
+Newcastle Knights and New Zealand Warriors, "CAN" both Canberra and Canterbury —
+so NRL matches favorites on team ID. Flattening every plugin to abbreviations
+would silently select the wrong club for NRL users. The base declares the seam,
+NRL fills it, and core never learns the string `"nrl"`.
+
+`CLOCK_COUNTS_DOWN` exists for the same reason in the opposite direction: a
+soccer clock reading `0:00` means the match has not kicked off, so running the
+clock-expiry branch there would evict live games.
 
 ## Phases