[om singhal (Om-singhaI)]

Fixes #2385

Node 24 calls uv_thread_setname("MainThread") at startup (src/node.cc on the v24.x branch; v25 uses node-MainThread). On Linux that sets the comm column from ps to MainThread. The picker then shows the process as MainThread and drops it unless it runs with --inspect.

procps also titles both the comm and command columns COMMAND, so indexOf('COMMAND') lands on the comm column. The parser takes the first word of comm as the command, and the PosixProcessTree step that looks for comm in the command line never sees the real one. The posix sample in src/test/node/process-tree.test.ts still passes only because it uses a BINARY header.

This change:

• finds the command column with lastIndexOf('COMMAND'). macOS heads comm with the aaaa string, so it has one COMMAND.
• falls back to argv[0] in PosixProcessTree when comm is not in the command line.
• also uses argv[0] when comm contains a space. That is a title like pm2's node <script>, and searching for it would swallow the whole line and hide the app.

On Linux the command is now the first word of the command line (say /usr/bin/node) and args no longer repeat it, as the posix sample test expects. Matching the node pattern in processPicker.ts instead would keep the MainThread label and change Windows and macOS too.

Tests: six procps style cases in src/ui/processTree/processTree.test.ts (plain node, Node 24 with and without args, Node 25, a pm2 app, a process that set its title). All six fail without the fix and pass with it. npm run test:unit goes from 305 to 311 passing. tsc --noEmit is clean, and so are eslint and dprint check on the touched files. A real macOS ps capture parses identically before and after. The Linux rows follow the procps output format, not a capture from a Linux machine.