docs: surface tracing and deep research in the README

[cyfyifanchen]

Problem

Raven now has two user-facing capabilities that are not visible enough in README.md:

• Observability tracing: raven tracing opens the bundled dashboard for captured LLM/tool/memory spans, and the TUI exposes /tracing.
• Deep research: raven deep-research configures the MiroThinker-backed deep_research tool, which can run longer research tasks when configured.

The README still leads with memory, self-improving skills, Agent Templates, proactivity, and self-evolution. Those are still correct, but the repo homepage does not show tracing or deep research in the quick capability scan, the command table, or the status/architecture surfaces.

Evidence

• raven/cli/tracing_commands.py registers the top-level raven tracing command and describes the local dashboard under raven/tracing/viewer/.
• ui-tui/src/app/slash/commands/ops.ts exposes /tracing as a TUI slash command.
• raven/config/raven.py has tracing enabled by default and documents RAVEN_TRACING=0 plus raven tracing / /tracing.
• raven/cli/deep_research_commands.py registers raven deep-research enable|get|reset for MiroThinker deep research configuration.
• raven/agent/loop/main.py wires configured deep research into the agent loop as the deep_research tool.

Suggested README updates

• Add tracing and deep research to the early capability list, likely under What You Can Do in 2 Minutes, Why Raven, Useful Commands, and Status.
• Consider adding a short observability row to the comparison table, e.g. captured spans for LLM/tool/memory/subagent activity vs opaque logs.
• Add raven tracing and raven deep-research enable|get|reset to Useful Commands.
• Clarify deep research is opt-in and provider/API-key backed, so readers do not assume it is always enabled or free.
• Mirror the key updates in README.zh-CN.md if the English README changes.

Acceptance criteria

• README.md makes tracing and deep research visible without requiring readers to inspect source code.
• The commands shown in README match the current CLI: raven tracing, /tracing, and raven deep-research enable|get|reset.
• The copy preserves the current positioning: Raven is still a self-improving agent harness, with tracing and deep research framed as additional harness capabilities.
• README.zh-CN.md stays consistent with the English README where applicable.