feat(zai): add GLM-5.2 with verified 1M context window

GLM-5.2 ships with a 1M (1,048,576) token context window. Without this
entry, Hermes falls through to the generic 'glm' key (202,752 tokens),
under-reporting the context bar and prematurely compressing conversations.

The 1M limit was verified empirically via needle-in-a-haystack retrieval
at 789,240 prompt tokens on api.z.ai/api/coding/paas/v4 — zero errors,
zero truncation, correct retrieval at every tested size (25K through 789K).

Changes:
- agent/model_metadata.py: add 'glm-5.2': 1_048_576 before 'glm' fallback
- hermes_cli/models.py: add glm-5.2 to zai curated models
- hermes_cli/setup.py: add glm-5.2 to setup wizard zai list
- hermes_cli/auth.py: add glm-5.2 to coding plan endpoint probes
- plugins/model-providers/zai/__init__.py: add glm-5.2 to fallback_models
- tests/agent/test_model_metadata.py: context resolution + vendor-prefix tests

agent/model_metadata.py

@@ -261,7 +261,13 @@ DEFAULT_CONTEXT_LENGTHS = {
     # https://platform.minimax.io/docs/api-reference/text-chat-openai
     "minimax-m3": 1000000,
     "minimax": 204800,
-    # GLM
+    # GLM — GLM-5.2 ships with a 1M context window (verified empirically:
+    # needle-in-a-haystack retrieval at 789K prompt tokens succeeded with
+    # zero errors on api.z.ai/api/coding/paas/v4).  Older GLM models
+    # (5, 5.1, 5-turbo) are ~202K.  Longest-key-first substring matching
+    # ensures "glm-5.2" resolves to 1M while older variants still hit the
+    # generic 202K fallback.
+    "glm-5.2": 1_048_576,
     "glm": 202752,
     # xAI Grok — xAI /v1/models does not return context_length metadata,
     # so these hardcoded fallbacks prevent Hermes from probing-down to