fix: cross-compile compat for codedb nuke

[justrach]

Replace std.c.getpid() with std.Thread.getCurrentId() so nuke command works on Linux cross-compile without libc dependency.

[github-actions]

Benchmark Regression Report

Threshold: 10.00%

Tool	Base (ns)	Head (ns)	Delta	Status
codedb_bundle	643726	648009	+0.67%	OK
codedb_changes	107167	108538	+1.28%	OK
codedb_deps	32784	29598	-9.72%	OK
codedb_edit	19348	19682	+1.73%	OK
codedb_find	137733	149609	+8.62%	OK
codedb_hot	170182	161082	-5.35%	OK
codedb_outline	448176	429216	-4.23%	OK
codedb_read	169699	167727	-1.16%	OK
codedb_search	260240	257737	-0.96%	OK
codedb_snapshot	3771055	3724749	-1.23%	OK
codedb_status	28030	27958	-0.26%	OK
codedb_symbol	65133	65102	-0.05%	OK
codedb_tree	140878	138906	-1.40%	OK
codedb_word	91842	89820	-2.20%	OK

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Compare kill list against a process ID

pgrep returns process IDs, but std.Thread.getCurrentId() returns a thread identifier, which is a different namespace on several targets (notably Darwin/Windows). That means the self-filter check later in this block is no longer reliable and can skip the wrong process or fail to exclude the current process when it is matched, causing nuke to terminate unexpectedly before cleanup completes. This should use a PID API instead of a thread ID.

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