Add bulk OLT PON flooding-mode tool; restore README; docs

Adds a second bulk workflow alongside the firmware upgrader: changing
PON flooding mode (private<->auto) on OLT NNI services across many OLTs.

Flooding mode is encoded by the presence of the "PON FLOOD ID" key on
each OLT-CFG["NNI Networks"] entry (present = private, absent = auto).
private->auto deletes the key; auto->private sets it to 0. The rest of
the OLT-CFG is preserved (PUT-as-replace, same as ONU-CFG).

- src/mcms-api.js: listAllOltConfigs / getOltConfig / putOltConfig, plus
  pure helpers floodModeOfNni, summarizeOltNniNetworks, planFloodChange
  (planFloodChange clones and never mutates its input)
- main.js: api:listOlts + api:executeFloodChange IPC handlers
  (concurrency 3, GET->plan->PUT, streams olt-flood:progress)
- preload.js: expose both channels + onFloodProgress
- renderer: OLT inspector view (#view-olts), two-step APPLY confirm,
  auto-saved pon-olt-flood-*.csv result report
- Restore README.md (lost to a filesystem error) and document the new
  feature in README.md and CLAUDE.md (new section 14)

Verified: npm run check passes; pure helpers unit-tested for the
no-mutation, idempotency, and rollback invariants.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

preload.js

@@ -26,6 +26,15 @@ contextBridge.exposeInMainWorld('api', {
 
   deleteOnus: (opts) => call('api:deleteOnus', opts),
 
+  listOlts: (opts) => call('api:listOlts', opts),
+  executeFloodChange: (opts) => call('api:executeFloodChange', opts),
+
+  onFloodProgress: (handler) => {
+    const fn = (_ev, payload) => handler(payload);
+    ipcRenderer.on('olt-flood:progress', fn);
+    return () => ipcRenderer.removeListener('olt-flood:progress', fn);
+  },
+
   fetchFecHealth: (opts) => call('api:fetchFecHealth', opts),
   fetchOnuSnapshot: (opts) => call('api:fetchOnuSnapshot', opts),
   savePlanCsv: (opts) => call('api:savePlanCsv', opts),