fix(deps): unblock the workspace resolution — align langchain to 1.x, drop dead providers

The fork's provider extras were pinned to a pre-1.0 langchain generation that
can't coexist with lfx's langchain-core 1.x, so `uv sync` (and CI) couldn't
resolve at all. Per the "route everything through hanzoai/ai" direction, the fix
is to align/drop rather than resurrect the provider zoo:
- langchain-openai >=1.1.12, langchain-anthropic >=1.0, pgvector >=0.4.2 (match lfx / cuga)
- dropped langchain-cohere (no core-1.x release exists; cohere is reached via the
  hanzoai/ai gateway, not a direct langchain integration)
- [tool.uv] environments pinned to linux (our deploy target; the macOS-only
  cuga/pgvector split is a separate dev-env concern)
- renamed the stale SDK module dir langflow_sdk -> flow_sdk (the rebrand renamed
  the pyproject refs + the pytest11 entry point but missed the directory, so the
  `flow` test plugin failed to import)

Verified: `uv sync` resolves + installs clean, and the IAM auth seam test now runs
in the REAL full-app env — 7/7 pass (previously only verifiable via direct module
load). This unblocks CI and all further flow work.

pyproject.toml

@@ -138,6 +138,7 @@ postgresql = [
 ]
 
 [tool.uv]
+environments = ["sys_platform == 'linux'"]
 override-dependencies = [
     # temporary force a newer python-pptx
     "python-pptx>=1.0.2",

src/backend/base/pyproject.toml

@@ -206,9 +206,9 @@ mongodb-vectors = ["langchain-mongodb>=0.11.0"]
 astradb = ["langchain-astradb~=1.0.0"]
 
 # Individual LLM providers
-openai = ["langchain-openai>=0.3.0,<1.0.0", "openai>=1.68.2"]
-anthropic = ["langchain-anthropic==0.3.14"]
-cohere = ["langchain-cohere>=0.3.3,<1.0.0"]
+openai = ["langchain-openai>=1.1.12,<2.0.0", "openai>=1.68.2"]
+anthropic = ["langchain-anthropic>=1.0.0,<2.0.0"]
+cohere = []  # routed via hanzoai/ai gateway (no langchain-cohere for core 1.x)
 google = [
     "langchain-google-genai~=4.1.2",
     "langchain-google-vertexai>=3.2.0",
@@ -270,7 +270,7 @@ markup = ["MarkupSafe==3.0.2"]
 aws = ["boto3>=1.34.162,<2.0.0", "langchain-aws~=1.1.0"]
 numexpr = ["numexpr>=2.10.4"]
 qianfan = ["qianfan==0.3.5"]
-pgvector = ["pgvector==0.3.6"]
+pgvector = ["pgvector>=0.4.2"]
 litellm = ["hanzo-llm>=1.60.2,<2.0.0"]
 zep = ["zep-python==2.0.2"]
 youtube = ["youtube-transcript-api>=1.0.0,<2.0.0"]
@@ -390,7 +390,6 @@ complete = [
     "hanzo-flow-base[astradb]",
     "hanzo-flow-base[openai]",
     "hanzo-flow-base[anthropic]",
-    "hanzo-flow-base[cohere]",
     "hanzo-flow-base[google]",
     "hanzo-flow-base[ollama]",
     "hanzo-flow-base[nvidia]",