Summary

Fixes #6186. Channels could only be added from the dashboard — the only mutating endpoint was POST /api/channels/sidecar/{name}/configure, with no inverse, so removing a channel meant hand-editing ~/.librefang/config.toml.

Changes

Backend (librefang-api)

• routes/sidecar_toml.rs — new remove_sidecar_block(path, name): removes the [[sidecar_channels]] block by name via toml_edit (preserving every other section's formatting), drops the sidecar_channels array key entirely when the last block goes, and writes atomically (same tempfile+rename scheme as upsert_sidecar_block). Returns whether a block was removed.
• routes/channels.rs — new DELETE /api/channels/sidecar/{name} handler: rewrites config.toml under the same config_write_lock that gates configure and POST /api/config/set, 404s when no matching block exists, then reload_config() + (on ReloadChannels) reload_channels_from_disk so the removed sidecar child process is stopped, not just dropped from disk. Registered in router() and openapi.rs.

Frontend (dashboard)

• api.ts / lib/http/client.ts — removeSidecarConfig(name) calling the DELETE endpoint.
• lib/mutations/channels.ts — useRemoveSidecarConfig with colocated channelKeys.all invalidation.
• pages/ChannelsPage.tsx — a confirm-guarded Trash button on each configured channel card.
• i18n keys added to en / zh / uk.

Scope decision

A removed channel's per-channel secret keys are deliberately left untouched: there is no remove_secret primitive today, and purging secrets is a separable destructive action. The confirm dialog states this. Wiring a secret-purge is a follow-up if wanted.

Verification

cargo check --workspace --lib                                  # ✓
cargo clippy -p librefang-api --lib -- -D warnings             # ✓
cargo test -p librefang-api --test sidecar_toml_test \
  --test channel_remove_test \
  --test dead_route_audit_test --test openapi_path_coverage_test   # all pass
cargo fmt --check                                              # clean

• sidecar_toml_test: remove_drops_named_block_and_keeps_others, remove_absent_name_is_noop_returning_false, remove_last_block_drops_the_array_key.
• channel_remove_test (TestServer): delete_removes_configured_sidecar_then_404s_on_repeat, delete_unknown_sidecar_404s.
• dead_route_audit + openapi_path_coverage confirm the new route is wired and documented.

pnpm typecheck          # clean
pnpm exec vitest run src/pages/ChannelsPage.test.tsx   # 19 passed (incl. new remove-flow test)
pnpm build              # ✓