P2poolv2 process management

[R27-pixel]

Summary

Adds start/stop/restart process management for the p2poolv2 node, mirroring the Bitcoin Core process management from #.

What's included

• New p2poolv2_path setting (falls back to PATH lookup when unset, same as bitcoind_path)
• p2pool_process_manager on App reusing the existing generic ProcessManager, with start/stop/restart/poll/shutdown
• Spawns the node with --config <p2pool_conf_path>, matching the real systemd unit's ExecStart
• New "Process" tab on P2Pool Status with [s] Start, [t] Stop, [r] Restart
• New "P2Poolv2 executable" field in Settings
• p2poolv2 now shuts down gracefully alongside Bitcoin Core on quit

Testing

• Unit tests for command construction, missing-executable failure, idle-stop no-op
• Unit tests for the new Settings field and Process tab key handling
• Render test for the Process tab

[codecov]

Codecov Report

❌ Patch coverage is 75.69036% with 537 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/components/bitcoin_status_view.rs	57.85%	169 Missing ⚠️
src/app.rs	60.09%	166 Missing ⚠️
src/main.rs	62.31%	78 Missing ⚠️
src/process_manager.rs	76.47%	56 Missing ⚠️
src/bitcoin_logs.rs	83.81%	39 Missing ⚠️
src/components/bitcoin_client.rs	96.03%	20 Missing ⚠️
src/components/p2pool_status_view.rs	93.02%	6 Missing ⚠️
src/components/status_bar.rs	91.89%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!

[R27-pixel]

Architecture Update

Since this PR was originally opened, the intended process-management architecture for PDM has changed following maintainer discussion.

The current implementation gives PDM direct ownership of the P2Poolv2 process through start/stop/restart controls and ProcessManager. We have since decided that PDM should not own the lifetime of the P2Poolv2 node.

The direction is to run P2Poolv2 as a systemd user service, with the service manager owning the process lifecycle. PDM will instead connect to an already-running node through its API and provide the relevant status and interaction functionality.

This means:

• P2Poolv2 continues running independently when PDM exits.
• PDM connects to an already-running P2Poolv2 node through its API.
• Process lifecycle is owned by the service manager rather than PDM.
• Docker/Podman remains a possible deployment option for the future.

This direction is being tracked in p2poolv2#289.

Given this, I think it's cleaner to close this PR and implement the service-based approach separately rather than refactor the current implementation. @pool2win, please correct me if I've misunderstood the intended direction before I close it.

[pool2win]

Agreed. Closing in favour of PR 289 as mentioned in the last comment.