Stats panel: Character | Mercenary tabs with merc skills

[errolgr]

Summary

Adds Character | Mercenary tabs to the advanced stats panel, so the merc's stats can be read without opening the merc inventory. The Mercenary page also shows the merc type and aura, max life, level, and a Skills box listing every merc skill with its level (total (base+bonus) when +skills apply) and the damage of its attack skill.

Problem

Today the panel shows merc stats only while the merc inventory (O) is open; as soon as it closes the panel switches back to the character. There is no way to see the merc's skill levels or what +skills items actually give the merc.

Changes

File	Change
BH/Drawing/Stats/StatsDisplay.cpp	DrawTabs: a Character | Mercenary strip at the top of the panel. Without a merc it reads Character | No mercenary (greyed, the click does nothing). The selected tab is kept when the panel is reopened; opening the merc inventory selects Mercenary as before.
	Merc page: Mercenary: Act N <aura> header, max life and level, in place of rows that don't apply to a merc.
	DrawMercSkills: a Skills box next to the main panel (left of it with statsOnRight): every named merc skill as Name: total, or Name: total (base+bonus) with +skills; plus the attack skill damage at the total level (physical and elemental).
	The main panel keeps the same size on both tabs (the old size-from-the-last-row logic is gone).
BH/Drawing/Stats/StatsDisplay.h	Tab rectangles/state, skills-box rectangle for InRange, declarations.
BH/D2Ptrs.h	D2COMMON_10121_GetMinElemDamage / 11091_GetMaxElemDamage for elemental skill damage.

• The Character page is unchanged.
• Expected conflicts with Stats panel: FBR breakpoints, physical pierce, and a side panel with more player stats #102: both PRs add fields to the StatsDisplay class and a box next to the main panel (Stats panel: FBR breakpoints, physical pierce, and a side panel with more player stats #102: side panel on the player tab, this PR: Skills box on the merc tab). Whichever lands second needs a small rebase; the two boxes are on different tabs, so they don't overlap.

Testing

In game (PD2 Season 13 client, single player): no merc, then an Act 1 Fire Arrow rogue hired from Kashya; each drawn line is compared with the server-side merc (skill levels, life, level, damage from #10567/#10297 and #10121/#11091). Then +2 all skills is put on the merc.

	Result
Before (current BH, and shipped PD2 BH)	no tabs; merc stats only with the merc inventory open
After (this PR)	all checks pass

Check	Drawn
No merc	Character | No mercenary (greyed)
Header	Mercenary: Act 1 Vigor
Skills	Vigor: 7, Fire Arrow: 7, Exploding Arrow: 7, Dodge: 5, Evade: 5
Attack damage	Fire Arrow: 25-69
+2 all skills	Vigor: 9 (7+2), Fire Arrow: 9 (7+2), Dodge: 7 (5+2), …, Fire Arrow: 40-90
Layout	every row inside the 600 px screen

Also checked by hand: Act 4 merc with the most skills (6) with +2 all skills: all rows fit.

Before (shipped BH): needs the merc inventory	After: Character tab

After: Mercenary tab + Skills box	After: +2 all skills (base+bonus)

After: no mercenary

Unit tests (native build of StatsDisplay.cpp against a fake engine): tabs, no-merc state, skills box rows and position, (base+bonus) formatting.

Runtime: 10/10 + 10/10 cold launches (PD2 and vanilla) with the branch build, no crashes. The other in-game scenarios have the same results as on main.

Full evidence: PR-EVIDENCE.md