Manage idle localhost servers and their process trees

[yxlyx]

Summary

• automatically move simple recognized localhost/dev-server commands (npm run dev, pnpm preview, next start, vite, python -m http.server, etc.) into supervised background jobs
• pause managed servers after 30 minutes of inactivity and stop them after 2 hours, with global environment overrides and a per-job keep_alive pin
• add bash_resume plus managed/paused/pinned/idle-stopped visibility in /jobs
• launch shell tools in their own POSIX process groups, so cancellation, timeout, bash_kill, idle stop, and session exit terminate npm/node/XCTest-style descendant trees rather than only /bin/sh
• document the lifecycle and configuration

Idle activity is deliberately local to the managed job: new stdout/stderr or an explicit bash_output/bash_resume call. Codegraff does not scan or interfere with unrelated localhost listeners.

Defaults can be configured with:

GRAFF_SERVER_PAUSE_MINUTES=15 GRAFF_SERVER_STOP_MINUTES=60 graff
GRAFF_SERVER_IDLE=off graff

Tests

• zig fmt --check on all changed Zig files
• zig build test (includes command-recognition/lifecycle tests and a process-group cleanup integration test)
• zig build -Doptimize=ReleaseFast
• cross-build: zig build -Dtarget=x86_64-linux -Doptimize=ReleaseFast
• cross-build: zig build -Dtarget=x86_64-windows -Doptimize=ReleaseFast
• generated graff --schema parses as JSON and includes bash_resume

Closes #199.
Related to #198.