fix: harden QOpen state and process boundaries

[CoderLambert]

Summary

• anchor the complete catalog, backup, recovery and replacement lifecycle to a trusted directory descriptor
• reject symlinks, hard links, special files, unsafe ownership/permissions and oversized state before parsing
• replace the pathname lock with a deadline-bound directory FD lock
• remove QML FileView and all StdioCollector usage in favor of bounded one-line backend responses and TERM-to-KILL deadlines
• run bounded helpers in isolated process groups so descendants cannot outlive helper deadlines
• add adversarial race, special-file, output-limit, timeout and bilingual-documentation coverage
• add explicit regression coverage for intermediate ancestor symlinks, concurrent backup-path replacement races, root-parent FD ownership and helper descendants
• add an explicit PathPicker refresh control plus F5 without introducing filesystem watchers
• keep ResourceEditor field sizing responsive while rendering complete four-sided form-field borders
• reject ambiguous bare single-label web targets while preserving domains, IPs, localhost and explicit-scheme intranet hosts
• document the security model and v2.5.1 upgrade behavior with precise runtime-vs-repair permission semantics

Marketplace review mapping

1. State paths now use component-by-component O_DIRECTORY/O_NOFOLLOW traversal, descriptor-relative O_NONBLOCK regular-file reads, same-directory temporary files, descriptor-relative os.replace, directory locking and fsync. Regression tests exercise an intermediate parent-directory symlink, a live config.json.bak regular-file/symlink race, and the /config.json root-parent FD ownership edge case.
2. QML no longer reads the catalog directly. The Python producer caps catalog/API/helper output before QML receives it; QML applies a secondary protocol-size check. Bounded helpers run in their own process groups and enforce real TERM-to-KILL deadlines across descendants.

Validation

• python -m json.tool manifest.json
• python -m py_compile bin/qopen
• python -m unittest discover -s tests -v — 46 passed
• qmlcachegen for all 5 QML components
• omarchy plugin validate .
• git diff --check
• read-only real-catalog check; SHA-256 unchanged before/after

[CoderLambert]

Runtime acceptance completed at exact HEAD bf7a352 on Omarchy 4.0.1 / Quickshell 0.3.1: the catalog rendered all 38 existing resources, collections rendered correctly, and the project add route opened the embedded non-GTK path picker. No new QML errors or Quickshell core dumps were observed. The personal catalog SHA-256 remained 40f3cecd5bc448a4b73e59c248a6bbd0fc9f45359d596b992dbd262fc54473f6 before and after all read-only checks. The installed copy was then restored to stable main.