feat: add token usage metrics and dialog

[mael-klingler]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds token usage metrics across three surfaces:

 1. TUI dialog (/usage slash command) — shows total/daily/per-session token breakdown and cost in the terminal UI.                                                                                                                                                                                  
 2. CLI command (opencode usage) — prints token usage summary from either the local DB or the remote console API, with optional --json output.                                                                                                                                                      
 3. Console backend — new /api/usage.json route and queryUsageMetrics server function that aggregate tokens by session/daily/weekly/monthly windows from UsageTable. The trackUsage function in the zen handler now also emits aggregate metric events (                                            
    session total, daily/weekly/monthly sums, estimated tokens-per-second).                                                                                                                                                                                                                         
                                                                                                                                                                                                                                                                                                    
 Also fixes a minor issue in src/index.ts where ResolveMessage was used as a type guard without being imported at runtime — replaced with a duck-typing check. 

How did you verify your code works?

Ran the TUI and opened the /usage dialog; ran opencode usage locally and confirmed token counts match session data.

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found two potentially related PRs that may be addressing similar functionality:

1. PR feat(opencode): first-class opencode insights usage report command #26590 - feat(opencode): first-class opencode insights usage report command

   • feat(opencode): first-class opencode insights usage report command #26590
   • This PR appears to add a usage report command, which is closely related to the token usage metrics feature being added in PR feat: add token usage metrics and dialog #28456.

2. PR feat(usage): unified usage tracking with auth refresh (#9281) #9545 - feat(usage): unified usage tracking with auth refresh

   • feat(usage): unified usage tracking with auth refresh (#9281) #9545
   • This PR deals with usage tracking, which overlaps with the token tracking functionality in PR feat: add token usage metrics and dialog #28456.

These PRs may be addressing similar or overlapping concerns around token/usage tracking and reporting, though PR #28456 appears to be more comprehensive (adding TUI dialog, CLI command, and console backend routes).

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[mael-klingler]

Thank you

[mael-klingler]

wie geht es nun weiter