feat: add normalized matching to memory search

[jif-oai]

Why

Memory search currently treats separators literally, so callers need to know whether a stored term uses spaces, hyphens, or no separators at all. That makes recall brittle for terms such as MultiAgentV2 vs. multi agent v2 and cold-resume vs. cold resume.

What changed

• Add an opt-in normalized mode to memory search that removes non-alphanumeric separators after any requested case folding.
• Thread the new flag through the MCP search tool into the local backend while keeping existing literal matching as the default.
• Reject queries that normalize to an empty string, and add regression coverage for both normalized matching and that validation path.

Testing

• cargo test -p codex-memories-mcp

[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Another round soon, please!

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