feat(web-ui): per-network connect toggle, one file for the Networks page - #685

The Networks tab strip carried a single ConnectButton that toggled ED2K and
Kad together, while each tab had its own state-blind Connect/Disconnect
buttons. That mirrored neither the REST API (already symmetric via
POST /networks/{connect,disconnect} with {network: "ed2k"|"kad"|"both"}) nor
amulegui after amule-project#663/amule-project#677, and it meant only the global button reflected the
actual connection state.

Each network tab now owns one state-aware toggle for its own network. Colour
and label follow the real state from the SSE status_changed event — a
red/amber/green plug reading "ED2K: Connected", "Kad: Connecting…" — while the
click performs the opposite action. "connecting" counts as up, so a Kad that is
running-but-not-routing (the backend collapses that into "connecting") stays
stoppable; this matches CKadDlg::OnBnClickedDisconnectKad. There is no
confirmation dialog, matching the buttons it replaces. Disconnecting both
networks at once is no longer offered.

Kad's "Connect from known clients" button is not lost: it issued the same
EC_OP_KAD_START the toggle does, exactly as amulegui's ID_KNOWNNODECONNECT
handler is a bare StartKad() call. "Bootstrap from node" is a genuinely
different operation (EC_OP_KAD_BOOTSTRAP_FROM_IP) and is untouched, as is the
per-row connect that dials one specific server.

The page is now a single view file. servers.js, kad.js, ed2k.js and logs.js
were imported by networks.js and nothing else, so splitting them only bought a
five-request, two-wave waterfall behind the lazy route import in app.js
RouteView — the browser had to parse networks.js before it could discover the
other four. At 410 lines the merged file sits alongside preferences.js (411)
and download-detail.js (429), which are single-file multi-tab views already;
Networks was the only page split up. split-detail.js stays separate, being
shared with Downloads and Shared files.

Merging also let some duplication and dead code go:

- stat() was defined identically in kad.js and ed2k.js; one copy remains, and
  the two log panels now share a logBox() helper.
- Three data.ensureStatus() calls in the panels were no-ops. Shell already
  calls it unconditionally for every route (app.js) and it is guarded by
  statusActive, so Ed2kInfoPanel no longer needs an effect at all.
- NetworkConnectButton lives in the view rather than components.js: it is
  Networks-only, and keeping it in components.js would have shipped it
  eagerly to every page.
- app.css: the button is now a .btn, so the tool-btn-derived sizing and the
  dead .tabs-extra .conn-btn overrides are gone. The state colours and
  .tabs-extra itself stay (still used by the Downloads category filters).
- i18n: no new keys — networks_tab_ed2k/_kad and app_connect* already cover
  the label. Eight keys left with no reference are removed, and the missing
  networks_kad_conn_disabled is added; without it the Kad info panel printed
  a raw key string whenever Kad was stopped.