v3.14.4 — expose all 8 z.ai GLM models

z.ai serves 8 GLM models; aigate was only exposing 3. This release
adds the missing 5 routes so the full z.ai catalog is reachable via
pibox-zai aliases. No removals, no breaking changes.

ADDED:
  - pibox-zai-glm-5.2     (newest flagship, released 2026-06-17)
  - pibox-zai-glm-5-turbo (fast tier)
  - pibox-zai-glm-5       (earlier 5-series)
  - pibox-zai-glm-4.6
  - pibox-zai-glm-4.5

PIBOX_AVAILABLE_MODELS default expanded to all 8.

QUOTA NOTE: z.ai bills the 5-series at 3x during Beijing peak
(14:00-18:00) and 2x off-peak (1x under the current promo through
end of September 2026). The 4-series bills at the flat 1x rate.
Defaulting to glm-5.2 burns subscription quota ~3x faster than
glm-4.7 during peak hours. docs/providers.md has the breakdown.

Patch bump — additive provider audit. Smoke clean for all 5 new
routes via litellm → pibox → z.ai.