fix: make activity history request-aware - #45

Summary

• derive Activity History Idle from persisted MCP request lifecycles instead of gaps between command rows
• keep current Idle first, pin all running command activity ahead of completed history before pagination, and handle parallel MCP requests correctly
• correlate commands from rolling-upgrade legacy Agents back to MCP using a privacy-safe SHA-256 execution-shape key
• stream MCP request state through the existing workspace activity realtime channel without restoring polling
• compact Activity History column widths so the table fits typical laptop viewports and long Input content uses the remaining width

Behavior

• process_start stops making the assistant look busy after the MCP response returns, even while the background process itself remains running
• no Idle row is shown while any MCP request is still waiting for a response
• historical Idle is derived from the union of MCP request spans and is only interleaved into chronological Started views
• command tools continue to have one visible command row; internal MCP request spans do not duplicate them in the table
• legacy AGENTPROC + tool="" command starts are normalized to MCP only when an unambiguous request correlation exists

Validation

• ./coderd/database/generate.sh (with the repo-supported dependency-check bypass for the broken local mise/yq check): PASS, including database gentest
• targeted Go tests for MCP lifecycle, Agent command activity/correlation, Activity query parsing, and correlation hashing: PASS
• compile-only pass for all touched Go packages: PASS
• Biome: PASS
• TypeScript tsc -p .: PASS
• targeted frontend Vitest: 44/44 PASS
• git diff --check: PASS

Environment limitation

Full DB integration/golden tests and the complete pre-commit target cannot run in this Developer Workspace because /var/run/docker.sock is absent. They fail while dbtestutil tries to start PostgreSQL, before exercising the changed SQL/test logic. The relevant generators, formatters, targeted unit tests, and compile-only checks above were run successfully.