feat: native AWS Bedrock provider via Converse API

Salvaged from PR #7920 by JiaDe-Wu — cherry-picked Bedrock-specific
additions onto current main, skipping stale-branch reverts (293 commits
behind).

Dual-path architecture:
  - Claude models → AnthropicBedrock SDK (prompt caching, thinking budgets)
  - Non-Claude models → Converse API via boto3 (Nova, DeepSeek, Llama, Mistral)

Includes:
  - Core adapter (agent/bedrock_adapter.py, 1098 lines)
  - Full provider registration (auth, models, providers, config, runtime, main)
  - IAM credential chain + Bedrock API Key auth modes
  - Dynamic model discovery via ListFoundationModels + ListInferenceProfiles
  - Streaming with delta callbacks, error classification, guardrails
  - hermes doctor + hermes auth integration
  - /usage pricing for 7 Bedrock models
  - 130 automated tests (79 unit + 28 integration + follow-up fixes)
  - Documentation (website/docs/guides/aws-bedrock.md)
  - boto3 optional dependency (pip install hermes-agent[bedrock])

Co-authored-by: JiaDe WU <40445668+JiaDe-Wu@users.noreply.github.com>

agent/model_metadata.py

@@ -1012,6 +1012,16 @@ def get_model_context_length(
         if ctx:
             return ctx
 
+    # 4b. AWS Bedrock — use static context length table.
+    # Bedrock's ListFoundationModels doesn't expose context window sizes,
+    # so we maintain a curated table in bedrock_adapter.py.
+    if provider == "bedrock" or (base_url and "bedrock-runtime" in base_url):
+        try:
+            from agent.bedrock_adapter import get_bedrock_context_length
+            return get_bedrock_context_length(model)
+        except ImportError:
+            pass  # boto3 not installed — fall through to generic resolution
+
     # 5. Provider-aware lookups (before generic OpenRouter cache)
     # These are provider-specific and take priority over the generic OR cache,
     # since the same model can have different context limits per provider