generic node commands

[daiagi]

Makes jam-ui a generic tool for any JAM client: every node is started from one shell command.

• --cmd '<command with {i}>' starts each node via sh -c, --nodes N sets the count (default 6); without --cmd or --logs it prints usage
• repeat --cmd to run different clients side by side, one node per command; a <label>= prefix titles the panes
• the Jamixir-specific paths are gone (hard-wired ../jamixir/node.sh, CARGO_MANIFEST_DIR, -x, .build.lock cleanup), so cargo install works
• --logs <dir> loads every *.log in the folder (minus summary.log), pane keys are 0-9
• summary.log is written when --summary-regex is given (capture group 1 = block hash)
• readme quickstart, changelog for 0.1.0, ci (build + test on ubuntu and macos)

Jamixir: jam-ui --nodes 6 --cmd 'cd ~/src/jamixir && ./node.sh {i}' --summary-regex '\[BLOCK\] ⛓️ Block created successfully\. Header Hash (.+)' (extra node.sh flags such as -x 4 go into the command)

Docker: jam-ui --nodes 4 --cmd 'docker run --rm --init --name jam-node-{i} <image> <flags>' (--init so containers stop when jam-ui quits)