Admin-configurable custom URI protocol handlers for autolinking

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Feature request

Allow administrators to configure which custom URI protocols (beyond http/https/ftp/mailto) should be automatically recognized and rendered as clickable links in Talk messages.

Only standard protocols are auto-linked in plain text messages. Custom protocols like e1c://, zoommtg://, tg://, ms-word://, jetbrains://, figma:// remain as plain text even though they are valid, OS-registered URI schemes.

Example:
e1c://server/1c-srv/235#e1cib/data/Document.Audit

→ Currently: plain text
→ Expected: clickable link

Proposed solution: Admin UI for protocol management

Structured list with validation (preferred)

Custom URI protocols

Protocol    | Description (optional)        | Actions
------------|-------------------------------|----------
e1c         | 1C Enterprise ERP links       | [Edit] [Delete]
zoommtg     | Zoom meeting links            | [Edit] [Delete]
tg          | Telegram app links            | [Edit] [Delete]
            |                               |
[+ Add protocol]

Security setting: [☑️] Only allow configured protocols (block all others)

Start by tracing Talk message autolinking and the existing standard-protocol allowlist, then inspect the admin settings entry point for adding configuration. Define how protocols are validated and stored, how configured schemes become clickable, and how the optional blocking setting behaves. Done means the admin can manage custom protocols and Talk messages consistently apply the selected policy.