fix(api): URL-encode searchText in chat.search

[Shreyas2004wagh]

Fix URL encoding in chat.search query params

Acceptance Criteria fulfillment

• Updated getSearchMessages to encode query parameters using URLSearchParams.
• Ensured user input in searchText is safely encoded (&, ?, #, %, +, spaces).
• Confirmed API package builds successfully after the change.

Fixes #1149

PR Test Details

• Ran: yarn workspace @embeddedchat/api build (passed).
• Verified generated request URL encodes reserved characters correctly in searchText.
• Confirmed no functional change for normal search inputs.

[Copilot]

Pull request overview

This PR fixes improper URL construction in the API wrapper by ensuring user-provided searchText is correctly URL-encoded when calling chat.search, preventing reserved characters from corrupting query parsing.

Changes:

• Updated getSearchMessages to build query parameters via URLSearchParams.
• Removed direct string interpolation of searchText into the request URL.

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