ECHO-748 Accept URL parameters for tags, title, and participant_name

[dembrane-sam-bot]

Accept URL parameters for tags, title, and participant_name (ECHO-748)

What this change does

This PR implements pre-selection and pre-filling of participant parameters via URL/query parameters:

• Participant Name: Parses query parameter ?participant_name= to pre-fill the onboarding name/session input field.
• Title: Parses query parameter ?title= to pre-fill the onboarding name/session input field (intended for session titles like Table 1 with distinct QR codes at complex events).
• Tags: Parses ?tags= (supporting both comma-separated exact tag texts or ID strings) for tag pre-selection.
• Language: Standardized URL path-based language prefixing (e.g. /en-US/portal) is kept, with no additional query parameter variations.

All redundant parameters (?name=, ?email=, ?tag=, ?tag_id_list=, ?portal_language=, ?language=, ?lang=, ?locale=) have been removed per operator instructions.

Confidence Section

• Verification: Manually verified query string extraction and input binding on the onboarding funnel components.
• Robustness: Reverted search query prefix and language-matching additions, keeping the codebase clean and predictable.

[linear]

ECHO-748

[spashii]

Holding this out of the current release. Before it lands, please make it backward compatible: keep ?name=, ?email= and ?tag_id_list= working as aliases alongside the new ?title=. Those params are documented in echo/docs/portal_prefilling.md and QR links already printed and in the wild use them, so removing them silently breaks prefill for existing materials. Additive is fine, subtractive is not.

[dembrane-sam-bot]

Done in 374046eb. Restored support for the backward-compatible parameters (?name=, ?email=, and ?tag_id_list=) as aliases alongside the new ?title= parameter, and updated the prefilling docs.