Add agent-friendly diagnostics reports

[AvdLee]

Summary

• Embed a structured JSON diagnostics payload in the single-file HTML report and render the browser UI from that payload.
• Write future session logs as structured records while preserving support for legacy HTML-fragment sessions already stored on devices.
• Add a repo-local Agent Skill with seed eval prompts for analyzing JSON-backed and legacy Diagnostics reports.

Test plan

• swift test

[Copilot]

⚠️ Not ready to approve

The current trimming order in LogsTrimmer.trim(data:) can remove newer structured log events before older legacy entries in mixed-format log files, which breaks expected “trim oldest first” behavior.

Pull request overview

This PR updates Diagnostics’ HTML report pipeline to be agent-friendly by embedding a structured JSON DiagnosticsReportDocument payload in the report and rendering the browser UI from that JSON, while also migrating session logs toward structured, JSON-line records with backward-compatible parsing of legacy stored HTML-fragment logs.

Changes:

• Embed a JSON report document (script#diagnostics-report-data) in the HTML output and render chapters client-side with updated functions.js.
• Introduce structured session-log models/records (DiagnosticsLogReport, DiagnosticsLogRecord) and a parser that supports mixed legacy + structured log storage.
• Add metadata/plugin descriptors and a repo-local “diagnostics-report-analyzer-skill” with eval fixtures.

File summaries

File	Description
Sources/Reporters/LogsReporter.swift	Switch logs chapter to return a structured DiagnosticsLogReport parsed from stored logs.
Sources/Logging/LogsTrimmer.swift	Update trimming to account for structured JSON-line log records (plus legacy trimming).
Sources/Logging/Loggable.swift	Emit structured JSON-line records for log writing; keep legacy HTML formatting logic as a separate path.
Sources/Logging/DiagnosticsLogReport.swift	Add structured log report/session/event models, record encoding/decoding, and mixed-format parser.
Sources/functions.js	Render the report UI from embedded JSON instead of pre-rendered HTML.
Sources/DiagnosticsReporter.swift	Generate HTML that embeds JSON and mounts a JS-rendered report root; add script-escaping helper.
Sources/DiagnosticsReportDocument.swift	Add JSON document schema for the embedded report payload and diagnostics-to-document value conversion.
DiagnosticsTests/*	Update/add tests for structured logs, mixed legacy+structured parsing, and embedded-report JSON extraction.
diagnostics-report-analyzer-skill/*	Add a support/debugging analysis skill plus eval prompts and fixtures.
plugins.json / package.json / openai.yml / agents/openai.yaml / .cursor-plugin/* / .claude-plugin/*	Add agent/plugin metadata for distributing the skill.

Copilot's findings

• Files reviewed: 23/23 changed files
• Comments generated: 2

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