fix(opencode): attribute sessions by agent id

[Haz3-jolt]

Purpose / Description

OpenCode session traces were not being populated because the CLI could install only an offline stub plugin, and auth login skipped OpenCode when the binary lived at ~/.opencode/bin/opencode instead of on PATH.

This PR moves OpenCode attribution to the harness-native active agent signal, resolves that name through the Observal lockfile, and sends the lockfile agent id and version to ingest.

Fixes

• Fixes: N/A, no issue number provided

Approach

• Move the real OpenCode telemetry plugin source into observal_shared so both CLI and server use one copy.
• Remove OpenCode plugin content from generated agent install snippets, since the plugin is installed by auth login or doctor patch, not per agent pull.
• Make observal auth login detect the official ~/.opencode/bin/opencode install path.
• Add OpenCode plugin version and content hash drift checks in doctor.
• Update doctor patch --all --harness opencode to install or update the plugin only when content differs.
• Attribute OpenCode sessions by active OpenCode agent name, then look up id and version from ~/.observal/lockfile.json.

How Has This Been Tested?

Learning (optional, can help others)

OpenCode stores sessions in SQLite at ~/.local/share/opencode/opencode.db, not JSONL. The plugin uses OpenCode runtime events and client APIs to export message objects into JSONL-compatible ingest lines.

The active top-level OpenCode session records an agent name, not an Observal UUID, so the reliable path is:

OpenCode active agent name -> Observal lockfile lookup -> agent id/version

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)

AI Assistance

Was generative AI tooling used to co-author this PR?

• Yes(Please Specify the tool): Pi coding agent
• Was the generated code manually reviewed and tested?

[codecov]

Codecov Report

❌ Patch coverage is 75.86207% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
observal_cli/cmd_doctor.py	86.36%	3 Missing ⚠️
observal-server/services/harness/helpers.py	0.00%	2 Missing ⚠️
observal_cli/cmd_auth.py	0.00%	2 Missing ⚠️

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