fix(cli): make every help string match what the CLI does (#1796)

[JarryShaw]

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Summary

pcapkit-cli's help strings in pcapkit/__main__.py did not match main() and Extractor. Each string was rewritten from probes of the real CLI; behaviour is untouched (an AST comparison with every help= masked is identical).

• Output: -o described the input file; it now gives the default out, the extension added only with --auto-extension, and the directory meaning under --files.
• Input and -a: the input help said .pcap is appended; that happens only with --auto-extension, and not for .pcap, .cap or .pcapng names. -a covers the input too.
• Format: -j, -p and -t each claimed to override all other options. The real order is -f, then -j, then -p, then -t, which is the default; each string now names what beats it. -f lists the accepted formats.
• The rest: -v, -F, -E, -P/-L, -B and -O now say what they do, and the grammar slips are fixed.
• Docs: the help block in docs/source/pcapkit/index.rst is regenerated from real --help at COLUMNS=80.
• Tests: tests/cli/test_main.py pins each corrected claim, including the precedence against main(). The new assertions fail on main's strings. tests/cli, the CLI subprocess tests and tests/project pass.

Closes #1796

[JarryShaw]

Verdict: GOOD TO GO at d3f1f5c76. A Sonnet cross-review and re-check (author: Opus). Each help string was probed against the real CLI in temp dirs: input with and without -a and .pcap/.cap/.pcapng, output with and without -a, and -F. The docs help block matches real --help output, and every new assertion fails on main's strings. tests/cli, the CLI subprocess tests and tests/project pass.

[JarryShaw]

The rendered-docs proofread (#1103) found more help strings with the same defect: -j, -p and -t each claim to override all other options (-f wins over all three), plus some grammar. A fix round is extending this PR. Fine to merge as is; if it lands first, the rest goes in a follow-up PR.

[JarryShaw]

Verdict: GOOD TO GO at 44a7738dd. A Sonnet re-check (author: Opus) probed every help string against the real CLI, including option precedence with -f, -j, -p and -t alone and combined. main() is unchanged (AST with help= masked), and the docs block equals real --help. The new tests fail on main's strings and against a branch-swap mutant. tests/cli, the CLI subprocess tests and tests/project pass.

[github-actions]

Coverage: 89.60% (unit tier, Python 3.15, 44a7738dd, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	2	20	2	96.77%
pcapkit/const	18862	954	2368	868	91.06%
pcapkit/corekit	2462	69	780	35	96.55%
pcapkit/dumpkit	276	3	100	3	98.40%
pcapkit/foundation	2915	164	1016	34	93.59%
pcapkit/interface	138	7	52	5	93.68%
pcapkit/protocols	17197	224	4580	189	98.09%
pcapkit/toolkit	872	177	298	8	77.18%
pcapkit/utilities	512	2	158	4	99.10%
pcapkit/vendor	4417	2342	1010	157	43.38%

Per-file detail: the coverage-html artifact of this run.