fix(npcs): grounded on real blocks, brighter avatars, per-NPC variety

[marceld23]

closes #711

Settlement/station NPCs floated half a block over the ground, rendered near-black, and looked like identical clones. Three fixes in one branch:

Grounding (server)

• The +0.5 hover was a regression from feat(worldgen): the worldgen overhaul — per-body identity, real seas, calibrated caves/ore, altitude climate, volcanoes #492: markers are converted to world space with a cell-centre +0.5, and the settlement spawner's Max(Min.Y + 1, markerY) clamp never fired. Spawn Y is now Floor()ed — the same fix the station-crew spawner already carried — while template upper-floor markers keep their storey. Bandit-camp guards get the same Floor().
• Bandits + planet enemies ground on real blocks now: they snapped to the pure noise SurfaceHeight, blind to stamped structures and player edits, so camp guards floated over their own carved camp floor. Both now use the creatures' GroundFeetYAt probe (Creatures are blind to real blocks: they walk through player-built walls and float over dug pits #650), falling back to the noise surface only when the chunk isn't loaded. Spawns use it too.
• Settlement NPCs re-ground each step (new TryGroundFeetYAt, capped at ±2 blocks): doorsteps lift them, mining the floor out from under them drops them instead of leaving them hanging forever. Unloaded/blocked columns fall back to the home marker's floor Y — never the noise surface, which inside a stamped settlement can be metres off.

Darkness (client)

• The tintable avatar textures average ~100/255 grey and LitColor computes _Color * tex, so every avatar rendered at ~40 % of its authored perceptual brightness. LoadTex now mean-normalises the texture toward ~200/255, keeping the pixel detail.
• The NPC outfit palettes were widened 3 → 6 tones per theme and lifted out of the mud; the client-side arms darkening eased 0.85 → 0.9.
• Bandit/Guardian materials never set _Floor/_Fill and ran at the shader defaults (0.35/0) — ~2× darker on the shadow side than every other humanoid (avatars/creatures use 0.62/0.3). They now share the standard lift.

Variation

• Per-NPC Size 0.92–1.08 (the wire field existed but was hardcoded 1f).
• Independent trouser colour via additive NetNpc.LegsRgb (contractless MessagePack; 0 = older server → client derives from the outfit as before).
• Android chassis tones vary, and only ~60 % of researchers are androids now (was: all of them, all one grey).
• Client-side deterministic per-NPC face jitter (eye spacing/brow/mouth/pupils) + hair (7 tones, some bald), seeded from NPC id + name through a stable hash — .NET string GetHashCode is per-process randomised and would have re-rolled every face each login.

Tests

• New regression guard: settlement NPC feet must land on the floored marker Y (would have caught feat(worldgen): the worldgen overhaul — per-body identity, real seas, calibrated caves/ore, altitude climate, volcanoes #492).
• Stroll-leash assert switched to horizontal distance (the code leash is XZ-only) plus a ±3-block vertical bound, since Y now legitimately tracks the floor.
• Full suite + Slow settlement tests green locally; Release build clean with -warnaserror; local Unity client build verified (client/Assets changed — PR CI doesn't build Unity).

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