Update dependency langchain-core to v1

[mend-for-github-com]

This PR contains the following updates:

Package	Update	Change
langchain-core (changelog)	major	==0.3.18 → ==1.2.11

By merging this PR, the below vulnerabilities will be automatically resolved:

Severity	CVSS Score	Vulnerability	Reachability
Critical	9.3	CVE-2025-68664	Unreachable
High	8.2	CVE-2025-65106	Unreachable
Low	3.7	CVE-2026-26013	Unreachable

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