Add optional Monocle observability (opt-in)

[imohammedansari]

Adds optional, opt-in Monocle observability to Open Deep Research, following the same app-owned env interface as the existing LangSmith tracing gate. Off by default; a default install is unaffected.

Env interface (parallel to LANGSMITH_*)

Variable	Purpose	Default
MONOCLE_TRACING	Truthy gate that turns tracing on	off
MONOCLE_EXPORTERS	Comma-separated exporters: file, console, okahu, s3, blob, gcs	file
OKAHU_API_KEY	Required only when okahu is selected	—

What it does

• The app reads MONOCLE_EXPORTERS itself, validates each entry against the known set, and fails fast on an unknown exporter or an okahu selection without OKAHU_API_KEY — before any instrumentation runs, so a config typo surfaces a clear error rather than an opaque one.
• It then forwards the value as setup_monocle_telemetry(workflow_name="open-deep-research", monocle_exporters_list=<MONOCLE_EXPORTERS or "file">). The app owns the exporter selection rather than deferring to Monocle's own env var.
• When MONOCLE_TRACING is unset/false the block is a no-op and monocle_apptrace is never imported.
• monocle_apptrace is an optional [monocle] extra (not a core dependency). Enabling tracing without the extra raises a clear install hint: pip install "open_deep_research[monocle]".

Each run writes one trace file to .monocle/, viewable in the Monocle VS Code extension; the okahu exporter sends traces to Okahu for cross-run analysis.

Files changed

• src/open_deep_research/deep_researcher.py — guarded, gated setup helper (initialized once at import).
• .env.example — MONOCLE_TRACING / MONOCLE_EXPORTERS / OKAHU_API_KEY block.
• pyproject.toml — monocle optional extra.
• README.md — "Monocle Tracing" section under Configurations.

Verification (4 cases)

• Disabled (default): module imports, monocle_apptrace never imported, setup not called.
• Enabled + installed: setup_monocle_telemetry called; MONOCLE_EXPORTERS=file,console → forwarded "file,console"; unset → "file".
• Enabled + extra absent: RuntimeError with the pip install "open_deep_research[monocle]" hint.
• Fail-fast: unknown exporter → ValueError; okahu without OKAHU_API_KEY → ValueError.

Also confirmed with the real installed monocle_apptrace that import open_deep_research.deep_researcher works both disabled (no .monocle/ written) and enabled (real setup runs).