fix: correlate log records with their span context

[alexhawat]

Description

OTel log records emitted by the plugin carried no context, so Logger.emit fell back to context.active() — which is always empty under opencode's event dispatch. As a result every user_prompt, tool_result, api_request/api_error, tool_decision, and session lifecycle log exported with no trace/span id and rendered as its own root trace in backends such as Logfire, instead of nesting under the session, run, tool, or LLM span that produced it.

Observed in a Logfire project (all parent_span_id = null):

span_name     kind  n
tool_result   log   2633
user_prompt   log   91

This resolves a context for every emitted log record:

• an explicit record.context always wins;
• otherwise the record is parented to the session/run context named by its session.id attribute (resolveLogContext);
• tool_result nests under its tool span, and api_request/api_error under their LLM span, by attaching that span's context.

The SDK honours LogRecord.context (const currentContext = logRecord.context || context.active() in @opentelemetry/sdk-logs), so the trace/span id now reaches the exporter.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Chore (dependency updates, etc.)

Checklist

• I have read the CONTRIBUTING.md document
• My code follows the style guidelines of this project
• bun run lint passes with no errors
• bun run check:jsdoc-coverage passes with no errors
• bun run typecheck passes with no errors
• bun test passes with no errors
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly (no doc change needed — comment-level only)
• My commits follow the Conventional Commits specification

Additional context

Tests added cover contextForSpanContext/resolveLogContext (explicit context wins, session/run resolution, unknown session fallback) and assert that the emitted tool_result and api_request records carry the tool/LLM span id. Full suite: 334 pass, 0 fail.

Related: #107, #109 (both concern trace-context propagation; this fix only covers the plugin's own log records).