feat: replace Langfuse with local-first tracing system

[anandgupta42]

What does this PR do?

Replaces the Langfuse SDK integration with a vendor-neutral, exporter-based tracing system. Every CLI and TUI session now captures full traces (generations, tool calls, tokens, cost, timing) as local JSON files with an interactive HTML viewer.

Core additions:

• Tracer class with FileExporter (local JSON) and HttpExporter (remote endpoints)
• 4-mode HTML trace viewer (Waterfall, Tree, Chat, Log) via Bun.serve
• altimate-code trace list and altimate-code trace view CLI commands
• Data engineering semantic attributes for warehouse/SQL/dbt/quality/cost
• Config schema: tracing.enabled, tracing.dir, tracing.maxFiles, tracing.exporters

Key design decisions:

• Crash-safe: writeFileSync in signal handlers, atomic tmp+rename snapshots
• Config-aware: TUI and CLI both honor tracing.* config settings
• Fail-safe: all tracing methods wrapped in try-catch, never crashes the app
• Localhost-only: trace viewer server binds to 127.0.0.1
• Session finalization: TUI traces end on session.status=idle

Type of change

• New feature (non-breaking change which adds functionality)

Issue for this PR

Closes #182

How did you verify your code works?

• 380 tests across 13 test files (unit, integration, adversarial, e2e)
• TypeScript type-check passes (0 new errors)
• Manual testing of trace list, trace view, and TUI /trace command
• 6-model code review (Claude, GPT 5.2 Codex, Gemini 3.1 Pro, Kimi K2.5, MiniMax M2.5, GLM-5) with convergence round

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[sentry]

Bug: A race condition in loadTracingConfig sets tracingConfigLoaded to true before async operations complete, causing subsequent calls to use uninitialized tracing exporters.
_{Severity: MEDIUM}

Suggested Fix

Move the tracingConfigLoaded = true assignment to after the await Config.get() call has successfully completed. Alternatively, use a Promise-based loading mechanism instead of a simple boolean flag to ensure subsequent callers wait for the configuration to be fully loaded before proceeding.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: packages/opencode/src/cli/cmd/tui/worker.ts#L61-L79

Potential issue: The `loadTracingConfig` function sets the `tracingConfigLoaded` flag to
`true` immediately upon entry, before an asynchronous `Config.get()` operation
completes. If a second call to `loadTracingConfig` occurs during this async window
(e.g., from a rapid `setWorkspace` call), it will see the flag as true and return
prematurely. This causes the second call's context to proceed with an `undefined`
`tracingExporters` variable, leading to the use of default tracer settings instead of
the user's configured exporters. Traces may be written to the wrong directory or sent to
incorrect endpoints.