feat: add mailing list frontend support (CM-1353)

[gaspergrom]

Summary

• Adds MAILING_LIST platform enum and identity configuration to enable mailing list activities and identities to display with platform icon and label across the frontend
• Follows existing patterns (groupsio as reference): minimal code, SVG icon, no integration card enabled
• Placeholder SVG icon included; final design asset must replace it before merge

JIRA

CM-1353 — Frontend: display support for mailing list integration

Notes

• QA Status: Filters (PASS), Integrations page (PASS), Icon placeholder (PASS), Design asset blocker noted
• Code quality: Minimal and follows established patterns
• Quality gates: lint ✅, build ✅
• Commit properly signed and formatted

Blocker: Icon asset from design must replace placeholder before merge (AC4)

[Copilot]

Pull request overview

Adds frontend display support for mailing-list activities and member identities.

Changes:

• Adds the mailinglist platform enum and identity configuration.
• Registers mailing-list labels, links, filters, and icon rendering.
• Adds a placeholder SVG asset pending final design.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
frontend/src/shared/modules/platform/types/Platform.ts	Adds the mailing-list platform enum.
frontend/src/config/identities/mailinglist/config.ts	Defines mailing-list identity display behavior.
frontend/src/config/identities/index.ts	Registers the identity configuration.
frontend/src/assets/images/identities/mailing-list.svg	Adds the placeholder platform icon.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 10 changed files in this pull request and generated no new comments.

[cursor]

PR Summary

Low Risk
Frontend-only identity/display wiring with no auth, API, or data-path changes; main follow-up is swapping the placeholder icon for the final design asset.

Overview
Adds Mailing List as a first-class identity platform so mailing-list activities and member/org identities can show the correct label, icon, and ordering alongside existing channels (pattern matches Groups.io).

Introduces Platform.MAILING_LIST (mailinglist), a new mailinglist IdentityConfig (member placeholder, activity links enabled), a placeholder envelope SVG, registration in lfIdentities, and MAILING_LIST placement in member and organization identity order configs (list, profile, suggestions).

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