fix(desktop): show private/forum icons in channel browser rows

[santhiprakash]

Fixes #6120.

Summary

The Add Channel dialog (ChannelBrowserDialog) rendered every row with a hardcoded # prefix, ignoring channel.visibility and channel.channelType. The sidebar already shows a lock for private channels and a file icon for forum channels; the channel browser drifted away from that and the same channel looked different in two surfaces of the same window.

This PR adds a pure, unit-testable ChannelRowIcon component with a getChannelRowIconKind() helper and uses it in ChannelBrowserDialog so the browser matches the sidebar's precedence (private → forum → #).

While this branch was open, main landed ChannelGlyph in SidebarSection via #6590, which also handles the project-home icon. Rebased on current main and left SidebarSection on ChannelGlyph to avoid duplicating or regressing that new behavior. ChannelRowIcon is now the browser-only icon, which keeps the PR focused on the reported bug.

Evidence

Checked against current main:

• ChannelBrowserDialog.tsx was emitting a literal # regardless of channel kind.
• SidebarSection.tsx now uses ChannelGlyph for the same visibility/type precedence (plus project home).

Reproduce

1. Create or join a private channel and a public channel in the same community.
2. Open the channel browser (Add channel).
3. Both rows show #. Nothing marks the private one as private.
4. The sidebar shows a lock on the private channel.

Expected

The browser row uses the same icon logic as the sidebar: lock for visibility === private, FileText for forum channels, # otherwise.

Testing

cd desktop && node --import ./test-loader.mjs --experimental-strip-types \
  --test src/features/channels/ui/ChannelRowIcon.test.mjs

6/6 pass. The helper is tested directly (getChannelRowIconKind) and the component is rendered under JSDOM + @testing-library/react to assert the right lucide-* class reaches the DOM for each channel kind.

tsc --noEmit -p tsconfig.json is clean.

Notes

• No screenshot: the icons are already present in the sidebar and the change makes the browser match it — the sidebar is the reference.
• File-by-file:
  • +desktop/src/features/channels/ui/ChannelRowIcon.tsx (new): 41 lines.
  • +desktop/src/features/channels/ui/ChannelRowIcon.test.mjs (new): 132 lines.
  • ~desktop/src/features/channels/ui/ChannelBrowserDialog.tsx: replace hardcoded # span with ChannelRowIcon.

[github-actions]

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