feat(forever): threat % text on nameplates and target/focus frames

[dfrisone]

What does this PR do?

Adds an optional threat percentage readout for WoW Forever, requested by Gingi, with the unit frame part added at Ellesmere's request:

• Enemy nameplates: your threat % on each enemy you are in combat with.
• Target and focus frames: your threat % on the unit, drawn inside the health bar.

Both are set from a new THREAT % TEXT section on the Forever Essentials > Threat page. Each has an on/off toggle, a Position dropdown (Inside Right / Left / Center), and a cog with Color by Threat, Size and X/Y offsets. The nameplate toggle is also available at the bottom of Enemy Nameplates > Threat Colors, since both write the same profile keys.

The number is the scaled threat percent, the same value the Threat Meter shows as Pull % (100% takes aggro).

Notes for review:

• Forever only (EllesmereUI.IS_FOREVER). The options rows are hidden on retail, and the runtime never shows the text there, even from a profile shared by a Forever character.
• On Forever, UnitDetailedThreatSituation returns the percent and the status as secret values for nameplateN tokens, while target and focus come back readable. The percent is therefore never read or compared in Lua; it goes straight to FontString:SetFormattedText.
• Nameplate coloring cannot use the four status colors, because the status is secret. It folds the isTanking flag through C_CurveUtil.EvaluateColorValueFromBoolean (the same approach as the existing off-tank color), so nameplates show the has-aggro color or the low-threat color. Target and focus use all four GetThreatStatusColor colors. With Color by Threat off, the text is white.
• Default position is Inside Right. That overlaps the health % text on Forever's default layout, so players who keep health % on the right will want Inside Center or a Y offset.

Implementation:

• Nameplates: the text is updated inside UpdateHealthColor, which the existing per-plate UNIT_THREAT_LIST_UPDATE already drives, so no new events. The FontString is created the first time a plate shows threat %, the same way as the focus letter (ns.EnsureThreatPctText), and ClearUnit only hides it on recycle if it was shown.
• Unit frames: a lazy watcher shaped like the Player Threat border: UNIT_THREAT_LIST_UPDATE for target/focus, PLAYER_TARGET_CHANGED, PLAYER_FOCUS_CHANGED and PLAYER_REGEN_ENABLED. It is registered only while the option is on, and restored at login only on Forever.

How was it tested?

WoW Forever client, open world, solo, tanking mobs:

• Nameplate threat % appears on mobs in combat with you and is red while you hold aggro.
• The target frame shows threat % with the four-color status coloring.
• Color by Threat off gives white text on both.
• Position, Size and X/Y update live.
• Turning either option off clears the text.
• Probed in game with issecretvalue: status and percent are secret on nameplate units, and readable on target.
• Retested on Forever after the review changes (lazy nameplate text, Forever-only login restore).

Not yet tested:

• the focus frame
• dungeons and raids
• a group, where the nameplate has-aggro vs low-threat color flip needs a second player
• the retail client (the feature is inert there)

Screenshots

WoW Forever, open world, solo tanking, both readouts at Inside Right. The nameplate shows 100% under the health %, and the target frame shows 100% beside it, both in the has-aggro color.

There is no before image, since this adds a new element.

Checklist

• New settings default OFF (no behavior change without opt-in)
• Zero cost while disabled: no events registered, no polling, no hooks doing work, no frames built. Nameplates cost one field read in the existing UpdateHealthColor, and no FontString exists until a plate first shows threat %. Unit frames build and register nothing until enabled.
• Cheap while enabled: event-driven (no polling, no timer-based logic, no per-frame allocations)
• No writes onto Blizzard-owned frames (weak-table pattern used); HookScript/hooksecurefunc only, never SetScript on Blizzard frames. All state lives on EUI's own plate and unit frames.
• Tested in-game on live; no version gates or pre-Midnight APIs added. Tested on the WoW Forever client only, as the feature is Forever-only. No version gates or pre-Midnight APIs.

[dfrisone]

Both addressed in e405d85:

• Nameplates: the threat % FontString is now created on first use by ns.EnsureThreatPctText, a clone of ns.EnsureFocusLetter, called at the top of ns.ApplyThreatPctPos. The pool constructor no longer builds it, and ClearUnit only hides it when _tptShown says it was shown.
• Unit Frames: the login restore is now EllesmereUI.IS_FOREVER and ....

Also merged upstream/main to keep the locale keys current. Retested on Forever.