docs(tts): A-Z order providers and add tools/tts to Tools nav group

- docs/tools/tts.md: alphabetize providers in three places that listed
  them: the supported-providers table (Azure Speech ... Xiaomi MiMo),
  the configuration Tabs (12 provider presets in A-Z), and the field
  reference AccordionGroup. Top-level fields stay first; provider
  tabs/accordions follow strict alphabetical order. Wording, schema,
  and defaults unchanged.
- docs/docs.json: add tools/tts to the main Tools sidebar group
  (slotted between trajectory and video-generation, matching the
  alphabetical neighborhood with image-generation, music-generation,
  video-generation). Previously tts only appeared under
  Nodes > Media capabilities, which was a discoverability gap for
  readers looking for TTS alongside the other generation tools.

docs/docs.json

@@ -1238,6 +1238,7 @@
                   "tools/tokenjuice",
                   "tools/loop-detection",
                   "tools/trajectory",
+                  "tools/tts",
                   "tools/video-generation",
                   {
                     "group": "Web browser",