Apply bow additional arrows to bow attacks

[unrealdreamz]

Summary

Refs #783.

Makes Bow Attacks fire an additional Arrow / Bow Attacks fire 2 additional Arrows apply to bow attacks' projectile count.

This intentionally does not multiply normal displayed hit DPS by arrow count. It only fixes the objective parser/matching issue that prevented the projectile-count modifier from matching current PoE2 bow skill flags.

Root Cause

The parser mapped Bow Attacks fire ... additional Arrows to KeywordFlag.Arrow. Current bow attacks such as Lightning Arrow receive ModFlag.Bow / bow weapon matching, but do not appear to set skillFlags.arrow, so these mods were filtered out before ProjectileCount was summed.

Fix

• Changed the bow-specific additional-arrow parser entries to use ModFlag.Bow.
• Kept generic arrow/projectile entries unchanged.
• Added a regression test proving the custom line increases Lightning Arrow projectile count with a bow equipped and does not affect a non-bow projectile spell.

Validation

Local, non-GUI validation only:

gh pr list --repo PathOfBuildingCommunity/PathOfBuilding-PoE2 --state open -S "783 bow attacks additional arrows projectile count" -> []
git diff --check -> passed
git diff --cached --check -> passed
git show --check --stat --oneline HEAD -> passed
where.exe lua -> not found
where.exe luajit -> not found
where.exe busted -> not found

I did not run Busted locally because this Windows checkout does not have Lua/LuaJIT/Busted on PATH. I also avoided Docker/GUI validation so no visible command windows or heavy processes were launched.

Risk / Rollback

Low risk. The change is limited to parser entries that explicitly say "Bow Attacks" and narrows matching to bow attacks via the existing ModFlag.Bow path. Rollback is this single commit.

[LocalIdentity]

user issue so this PR does not apply