docs: fill coverage gaps across API reference, CLI, Omni, and app dev guide

[kenvandine]

API reference:

• openai.md: document enable_thinking/thinking params for reasoning model control;
  add SSE streaming client-side guidance (reconnection, cold-start, error handling)
• lemonade.md: add GET /v1/system-stats, POST /v1/log-level, POST /v1/params
  endpoint sections with request/response examples; add sdcpp_args, flm_args,
  and vllm_args to the /v1/load parameters table; update summary table
• anthropic.md: expand from a 2-line stub to a full API reference with parameter
  table, curl + Python SDK examples, non-streaming and streaming response formats,
  and error response table

CLI reference:

• cli.md: add lemonade config to the Server commands table and ToC; add
  "Options for config" section with examples and link to /v1/params

Omni/collection docs:

• lemonade-omni.md: add REST API section for collection create/query/delete;
  document component loading behavior and LRU eviction implications; add
  chat-transcription model guide covering when to use native multimodal models
  vs OmniRouter, message format, and label-based discovery

New app developer guide:

• building-apps.md: new guide covering connection pattern, model discovery,
  inference examples (chat, embeddings, images, audio), streaming best practices,
  runtime model management, error handling reference table, authentication, and
  performance tips
• dev/README.md: restructure to surface building-apps.md and examples index for
  app developers alongside the existing contributor docs

https://claude.ai/code/session_01RZAtERd26JPV38HTa8Sj9d

[jeremyfowers]

Yeah, something like this is probably needed. We need a whole "SDK" landing page tbh.

[fl0rianr]

Thanks for filling these docs gaps — the new app-dev guide is good, but I think this needs a small cleanup before merge:

• /v1/log-level is documented as requiring LEMONADE_ADMIN_API_KEY, but it is registered as a regular /v1/* route. With only LEMONADE_ADMIN_API_KEY configured, regular API routes are still unauthenticated, so this doc currently overstates the protection. Either move this to /internal/* or document the actual auth behavior. I think Jeremy's comment was not addresed.
• The CLI docs say lemonade config uses POST /v1/params, but the CLI calls /internal/set.