microagent v0.15.0

Added

• The top-level config key reasoning_effort sets the same optional reasoning
  level as --reasoning-effort. The flag overrides MICROAGENT_REASONING_EFFORT,
  which overrides the file; omitted or empty keeps the provider's default.
  OpenCode receives its native reasoning_effort field, or thinking.type
  set to disabled for none.

Fixed

• Preserve streamed reasoning_content on assistant messages so OpenCode Zen
  and Go thinking models can continue after tool calls and across REPL prompts.
  Reasoning shares the response byte ceiling and is kept out of stdout and
  session logs; a stream failure after reasoning is generated is not retried.
  Document both gateway base URLs, bare model IDs and the Chat Completions API limit.

• Send a stable x-opencode-session header to OpenCode for each conversation;
  Go otherwise rejects requests with MissingSessionID. Decode compressed
  provider error bodies so their reason is readable instead of compressed bytes.