feat(web): add collapsible connections list pane (desktop icon pattern)

[deviationist]

⚠️ Alternative to #2047 — same feature, different presentation.

#2047 introduced the connections-list collapse with a single floating rotating chevron. This PR is the same feature implemented with the desktop icon pattern instead, per @ysfscream's review suggestion on #2047 ("could we align this with the existing desktop UI pattern? Desktop uses icon-hide-connections in the connections list header and icon-show-connections in the detail header when the list is hidden").

Summary

Brings the desktop app's "show/hide connections list" feature to the web build. The connections list pane on the left can be collapsed to give more horizontal space to messages, subscriptions, and the publish editor — useful for long topic trees or wide payloads.

State is persisted into the existing db lowdb store under settings.showConnectionList — the same JSON blob in localStorage that already holds currentTheme, currentLang, autoCheck, etc. — so the layout sticks across reloads.

Behavior

• Desktop icon pattern: icon-hide-connections lives in a flex topbar next to the list's connections titlebar; icon-show-connections renders inside the detail header (.connection-head, before the title) with v-if="!showConnectionList". Mirrors src/views/connections/ConnectionsList.vue:24-41 and src/views/connections/ConnectionsDetail.vue:13-31 on desktop.
• From the form (?oper=create / edit) and empty-state views, the recovery path is the Leftbar connections icon — matches desktop, which also doesn't render a show-button on those views.
• The Leftbar's connections icon is route-aware: on /recent_connections or any of its subpages (/recent_connections/:id, including the ?oper=create form), clicking it toggles the pane in-place; from settings/help/about it routes to /recent_connections as before without toggling. You can collapse/expand the list without leaving the connection you're viewing or editing.
• All affected layout offsets (.right-topbar, .connections-detail-main margin, .filter-bar, the subscriptions LeftPanel, plus the marginLeft getter that accounts for showSubs + largeDesktop) reflow with 0.3s cubic-bezier(0.4, 0, 0.2, 1) transitions.

Note on one small divergence from desktop

On the desktop app, the show-button only lives inside ConnectionsDetail.vue — there's no show-button on the empty-state view or the create/edit form. So on desktop, if a user has zero registered connections and hides the list, they can't bring it back until they add at least one connection. The pane stays hidden through the entire onboarding flow.

This PR matches desktop's icon placement exactly (no show-button on the empty-state or form views either — src/components/EmptyPage.vue and src/views/connections/ConnectionForm.vue are unchanged). What does differ: web's Leftbar connections icon is now route-aware (see web/src/components/Leftbar.vue change), so on /recent_connections* — including the empty-state view — clicking it toggles the pane. Net effect: visually aligned with desktop on the icons; slightly more forgiving on recovery from empty-state because the Leftbar gives users a way out. Keeping that small asymmetry — happy to remove it if reviewers prefer strict parity.

Why this exists in desktop but not web

The desktop variant (src/) already has this feature (showConnectionList in store/modules/app.ts, iconfont icon-hide-connections / icon-show-connections in ConnectionsList.vue and ConnectionsDetail.vue). The web variant (web/src/) shipped without it — the .left-list div in web/src/views/connections/index.vue had no toggle, no Vuex state, and no buttons. This PR closes that parity gap, and unlike #2047 it also matches desktop on the presentation layer.

Files

File	Change
web/src/store/modules/app.ts	showConnectionList state, TOGGLE_SHOW_CONNECTION_LIST mutation + action; persists via setSettings('settings.showConnectionList', …) so it lives in the existing db lowdb store alongside theme/lang/etc. — no extra top-level localStorage key
web/src/database/index.ts	showConnectionList: boolean added to the settings schema, with a default of true on first run
web/src/store/getter.ts	new showConnectionList getter
web/src/types/global.d.ts	App.showConnectionList: boolean
web/src/lang/connections.ts	hideConnections / showConnections (zh, en, ja)
web/src/views/connections/index.vue	flex .left-list-topbar with hide-button, layout overrides, transitions
web/src/views/connections/ConnectionsDetail.vue	show-button in .connection-head, TOGGLE_SHOW_CONNECTION_LIST action wired, marginLeft getter accounts for hidden list
web/src/components/Leftbar.vue	route-aware toggle on the connections icon

Test plan

Verified locally so far: light, dark, and night themes — both icon-hide-connections and icon-show-connections render correctly in all three (color follows var(--color-text-title), hover state preserved). Also verified the lowdb migration: existing users without settings.showConnectionList get it seeded to true on first load.

• Hide-button in the list's titlebar — clicking slides the list out, detail/empty/form pane fills the freed space
• Show-button appears in the detail header (.connection-head, before the title) when the list is hidden — clicking restores the list
• On /recent_connections (list view), click the Leftbar connections icon → toggles in place
• On /recent_connections/:id (connection detail or ?oper=create form), click the Leftbar connections icon → toggles in place without navigating away
• From the empty-state and form views with the list hidden, the Leftbar connections icon restores the list
• Reload the page — showConnectionList state restored from db.settings.showConnectionList (inspect the db entry in localStorage to confirm there's no separate showConnectionList key)
• With a connection open and subscriptions visible, toggle — filter bar, footer, message list, and subscriptions popup all reflow smoothly
• Switch to settings / help / about with list hidden — return via the Leftbar connections icon → routes there without changing the toggle state
• Try at <1920px and ≥1920px viewports — offsets adapt for both breakpoints
• Light / dark / night themes — both icons follow var(--color-text-title)

Screenshots

[ysfscream]

Thanks for the update, this looks good.