manager: universal footprint rule — already-quantized (cached) models measured as-is, no quant factor

Per directive: the VRAM estimate must always equal the model's ACTUAL full pipeline
footprint, by a universal rule rather than per-model tuning. The quant factor exists
to convert an UNQUANTIZED source's weight size down to its quantized runtime size —
so it must NOT be applied to weights that are ALREADY quantized on disk.

Add _quantized_cache_gb(): find this model's quantized pipeline cache by MODEL NAME
(glob '<safe_name>__*', ignoring in-progress '.building' dirs; signature suffix
drifts with trivial config edits, so name-match is the robust signal) and return its
real on-disk size. _get_model_used_vram_gb now, right after the forced-measurement
check, returns that cache size AS-IS (+ reserve) when present — no quant_mult, no
precision factor. The cache holds already-quantized weights, so its size IS the
footprint, and it overrides a stale used_vram_gb (e.g. Wan2.2-I2V's 151 GB fp32 disk
size). Models quantized AT LOAD (no cache yet) still fall through to the factor-based
estimate. Verified: VACE-Fun now estimates ~24 GB (real 4-bit footprint) instead of
24.5 x 0.283 = 6.9 GB, so eviction frees the idle image model before the forward.

Reverted the per-model measured_vram_gb pin in models.json — the universal rule
covers it.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RdMufYvtTbtGDWsiZVoXce