feat: add in-session workflow nudges

[ccf]

Summary

• add sidecar-first in-session workflow nudges that combine live session signals with session-start coaching
• expose a new MCP tool for actionable nudges during an active local session
• mark the roadmap item for in-session workflow nudges shipped

Testing

• PYTHONPATH=src pytest tests/test_nudges.py tests/test_mcp_tools.py tests/test_mcp_server.py -q
• ruff check src/primer/common/schemas.py src/primer/mcp/nudges.py src/primer/mcp/tools.py src/primer/mcp/server.py tests/test_nudges.py tests/test_mcp_tools.py tests/test_mcp_server.py
• ruff format --check src/primer/common/schemas.py src/primer/mcp/nudges.py src/primer/mcp/tools.py src/primer/mcp/server.py tests/test_nudges.py tests/test_mcp_tools.py tests/test_mcp_server.py

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Note

Medium Risk
Introduces a new sidecar-facing MCP tool that combines local live-session signals with a server-fetched coaching brief; behavior depends on signal mapping logic and tolerating invalid/failed coaching responses.

Overview
Adds in-session workflow nudges to the Primer sidecar: new Pydantic schemas (InSessionNudge, InSessionNudgesResponse) and a build_in_session_nudges mapper that turns specific live signal types into prioritized, action-oriented suggestions (with a low-risk “stay the course” fallback).

Exposes this via a new MCP tool in_session_nudges (and primer_in_session_nudges) that pulls local live-session signals, optionally fetches the session-start coaching brief from the server, and renders a markdown nudge report; invalid coaching payloads or request errors are handled by falling back to nudges built from live signals only.

Marks the roadmap item for in-session workflow nudges as shipped and adds focused tests for the new nudge builder and MCP wiring.

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