feat(common): sports_celebration, sports_fetch and sports_card_wrappers, promoted from the scoreboards (sports consolidation stage 3) (#672)

Three new hardware-free modules holding code the scoreboard plugins carry
as identical copies (executable AST, docstrings stripped, checked across
every carrying plugin at ledmatrix-plugins 30455671). The bodies are the
plugins'; the changes are type annotations for the mypy ratchet, the
colour helpers losing their leading underscore as public free functions,
and two comments that described the plugins' files.

- src/common/sports_celebration.py: SportsCelebrationMixin, the score/win
  takeover drawn by afl, football, hockey, nrl and soccer
  (_draw_celebration_layout and the palette, backdrop, scenery, confetti,
  crest and _fit_font steps, with their class constants), plus the colour
  helpers (logo_palette, lift_color, cap_luminance, mix_color, ...). Only
  the drawing: _start_celebration, _check_for_goal/_check_for_score,
  _check_for_win and display() differ between the plugins and stay there.
- src/common/sports_fetch.py: SportsFetchMixin, the four SportsCore methods
  identical in all nine scoreboards: _fetch_season_directly,
  _background_fetches_espn_ranges, _needs_previous_day and
  _wants_live_odds, with _LOOKBACK_CUTOFF_HOUR and _LIVE_ODDS_LOOKAHEAD.
  _get_timezone, _extract_game_details and _fetch_data are as identical
  and stay behind, for the reasons sports_shared gives (a per-plugin
  import; the abstract contract); so does SportsUpcoming.__init__, since
  no src/common mixin has a constructor.
- src/common/sports_card_wrappers.py: SportsCardWrappersMixin, the
  seventeen sports_card delegations the eight game renderers carry (15 in
  all eight, 2 in all but football, whose own versions override them).
  _schema_font_size/_resolve_font_size look identical but read each
  plugin's own _SCHEMA_PATH, so they stay.

Each mixin has no __init__ and creates no attributes (the host contract is
declared as annotations only), defines no name the mixins beside it
define, and documents the attributes it reads; a host-contract test
parses each and fails on an undocumented read. A method kept on a
plugin's class wins over the mixin's.

Tests: behaviour ported from the plugins' celebration, odds, lookback and
date-range tests against stub hosts carrying exactly the contract, with
crests drawn by the test (test_sports_celebration.py, test_sports_fetch.py,
test_sports_card_wrappers.py), and test_sports_stage3_parity.py, which with
LEDMATRIX_PLUGINS set compares every body with every plugin copy that is
left (58 pass against the plugins today; a copy that is gone counts as
adopted). All three modules are on the mypy ratchet, in
src/common/README.md, the CHANGELOG's Unreleased section and
SPORTS_UNIFICATION's module table. Nothing in core uses them yet.

Full suite: the same 67 failing test ids as main (Windows-only), 77 more
passing.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/SPORTS_UNIFICATION.md

@@ -83,6 +83,9 @@ more. Shared sports code lives in `src/common`:
 | `espn_dates.py` | 3.5.0 | ESPN date-range and `limit` workarounds |
 | `favorite_team_check.py` | 3.6.0 | `FavoriteTeamCheck` — logs why a favourite team code shows nothing |
 | `sports_timezone.py` | 3.6.0 | Which timezone start times are drawn in (`resolve_timezone_name`) |
+| `sports_celebration.py` | Unreleased | `SportsCelebrationMixin` — draws the score/win takeover; colour helpers |
+| `sports_fetch.py` | Unreleased | `SportsFetchMixin` — season fetch, live lookback and live-odds decisions |
+| `sports_card_wrappers.py` | Unreleased | `SportsCardWrappersMixin` — the game renderer's `sports_card` delegations |
 
 Each is described in [src/common/README.md](../src/common/README.md).
 
@@ -168,6 +171,15 @@ Mix it in **before** the mode class — `class SoccerLive(CelebrationMixin,
 SportsLive)` — so the celebration `display()` runs first and falls through to
 the scorebug via `super()`.
 
+What shipped is narrower. `src/common/sports_celebration.py`
+(`SportsCelebrationMixin`) holds only the drawing, which is identical in the
+five scoreboards that celebrate (afl, football, hockey, nrl, soccer — hockey
+grew celebrations after this was written). Arming a celebration stays in each
+plugin: the trigger bodies differ (nrl matches favourites by team id, football
+folds a touchdown's extra point into one celebration and picks scenery by
+points), and so does `display()`. The seams above were not needed to move the
+drawing, so none was added.
+
 **Rotation strategies.** The three "dialects" turned out to be one algorithm
 (Smooth Weighted Round-Robin) in two shapes: an incremental picker holding state
 across calls (afl/nrl/soccer) and a precomputed per-cycle list