Add skeleton archer

[AtlantisPleb]

Summary

• Add a ranged unit: a Skeleton Archer that shoots physical projectiles (arrows) from a bow.
• Use the SRD Skeleton stat block as the basis for attributes and defenses; attacks are ranged bow shots per SRD (no burning or magic effects).

Goals

• Server-authoritative behavior only; client is presentation.
• Ranged engagement: prefers to attack at distance, minimal melee logic.
• Deterministic projectiles and damage; respect existing perf/determinism rules.

Acceptance Criteria

• A new Undead archetype “Skeleton Archer” spawns and uses a bow-like ranged attack that fires a projectile toward targets within range.
• Projectile behaves like a physical shot (no DoT, no burn); applies damage on hit and despawns.
• AI engages at range: will stand and fire when in range and line of fire; no kiting required in v1.
• Uses SRD Skeleton stats (HP/AC/speeds/traits/resistances) and ranged attack profile. Ensure NOTICE and SRD docs are updated when stats are committed.
• Unit tests cover: projectile spawn, hit/damage application at range, snapshot correctness.

Tasks

• Data/schema
  • Add an archetype entry for SkeletonArcher under data_runtime (stats sourced from SRD Skeleton).
  • Add a projectile spec for Arrow (speed/ttl/damage) if we model arrows as projectiles distinct from spells.
• Server_core
  • Add ProjKind::Arrow (or reuse Firebolt path with no burn) and specs in projectile_spec().
  • Hook Arrow into projectile integration/collision (no special AoE; single-hit segment/cylinder like Bolt).
  • Add a simple ranged AI path that, when hostile and in range, enqueues an Arrow shot at its target.
  • Ensure ActorSnapshot v2 continues to exclude projectiles from actors and carries Arrow in projectiles.
• Renderer/HUD (minimal)
  • No new VFX required for v1; re-use existing hit FX or add a tiny impact spark if desired.
  • Ensure HUD damage/HP bars reflect server replication only.
• Tests
  • Arrow hits hostile at range: spawns, steps, damages target, projectile despawns.
  • Snapshot contains no lingering Arrow projectiles after hit.

Notes

• Do not copy SRD text directly into code; implement values per SRD and ensure proper attribution (NOTICE and docs/gdd/03-srd/*) when stats are added.
• If we later add a specific skeleton archer model/animation, track that in a separate asset issue and keep this issue focused on server behavior + minimal presentation.