fix(channels): remove duplicate Modal import

[bolichen97]

Problem / Motivation

Main no longer typechecks after #5570 added a second default import for Modal in ChannelPage. The same symbol was already imported by #6796, so TypeScript fails deterministically with TS2300 at lines 2 and 16.

Why it matters

This is a main-branch compile regression and makes unrelated PRs fail the frontend typecheck gate.

What changed

Remove only the later duplicate import. The original shared Modal import and all Channel behavior remain unchanged.

Tests

• red-before: npm run typecheck fails deterministically with duplicate identifier Modal
• fixed final main snapshot: npm run typecheck passes
• ChannelPage coverage, clear-context, IME, menu-keyboard, and narrow-layout suites: 106/106 passed
• changed-file ESLint and diff checks pass
• audited all open PRs: the only exact-file overlap, fix(channels): per-command trust tiers on approval cards (#5231) #5248, changes approval trust tiers and does not own this import regression

No retries, sleeps, timeout changes, warning filters, or assertion changes were added.

Screenshot evidence

Why no screenshot: This removes a duplicate import only; runtime UI output is unchanged.