Add opt-in seasonal item colours and gear sorting

[andybergon]

What does this PR do?

Draft feature proposal, dependent on #2093. This branch includes that prerequisite until it merges; the additional feature is commit 6b72885.

Add two opt-in controls for bag equipment categories:

• Season-aware colours, off by default: current seasonal gear keeps track colours, untracked item-level text becomes white, and an additional off-by-default option greys recognised previous-season gear. Bank item-level colours follow these choices. Custom colours take priority.
• Gear sort order: track then item level (unchanged default), current season then track, current season then item level, or item level then track. Blizzard bank and MultiBag sorting are unchanged.

The purpose is to distinguish useful current gear from older collections without confusing rare-quality blue with Champion track colouring. Season means recognised seasonal upgrade/crafting bonuses, not everything acquired during a season. Unknown gear is not labelled as previous-season gear.

This stays draft during the feature freeze. The Midnight S1/S2 bonus lists require maintenance for later seasons. The master colour toggle keeps existing defaults intact.

How was it tested?

• In-game screenshots verify the grey treatment, white untracked text, and Season > track ordering, including a current 321 Hero chest before an old 289 Myth chest.
• Lua 5.1 syntax checks and 177 colour assertions, plus actual sort/cache and settings callbacks for all four modes. Master-off tests preserve old track colours and rarity fallbacks. Independent Claude follow-up confirmed both earlier High findings were resolved; no concrete defect survived.
• Screenshots precede the new master toggle and fixed craft sort priority. Bank colours, Hero crafts, the two item-level-priority modes, master-toggle UI, and widened dropdown still need live verification. Tests are local mocks, not CI or native-client proof.

Screenshots

Optional previous-season grey text

Before:

After:

Optional season-first sorting

Before: the old 289 Myth chest precedes the current 321 Hero chest.

After Season > track:

White text for untracked gear

Before: untracked 259 items use rarity blue.

After: untracked 259 items use white text; current tracks and grey older gear remain distinct.

Checklist

• New settings default OFF; existing track-first sorting remains the default.
• Zero cost while disabled: no new events, polling, hooks or runtime frames; optional seasonal classification runs only when needed.
• Cheap while enabled: event-driven refreshes, bounded sort cache, no polling.
• No new writes or scripts on Blizzard-owned frames.
• Tested in-game on live; no version gates or pre-Midnight APIs added. Partial coverage and remaining checks are documented above.