[vmvarela]

Summary

--inspect sample N and --inspect=sample N treated the count N as a positional
input filename, so e.g. sql-pipe --inspect sample 2 failed with cannot open file '2'
(exit 2) instead of printing the schema plus 2 rows.

The parser now consumes an immediately following positive integer as the sample count
for both canonical --inspect syntaxes, using exactly the same rules the deprecated
--sample flag already used: flags and -- are not consumed, non-numeric names are
left as file arguments, and 0 is a usage error (stderr diagnostic sample count must be a positive integer (--inspect sample or --sample), exit 1). To sample a file whose
name is a number, use ./N or put it after --.

• Regression tests added first in build.zig (9 new Bash integration tests); the five
  behavioral ones (--inspect sample 2, --inspect=sample 2, count-not-file with
  --no-stdin, zero-count usage error, missing-source diagnostic with count) failed
  against the unmodified source (exit 2 / default count) and pass after the fix.
• Documentation updated only where the sample-count contract is described: CLI help
  (src/args.zig, example changed from --sample 5 to --inspect sample 5), README
  inspect section and --inspect table row, and the man page source
  (docs/sql-pipe.1.scd).
• Deprecated --sample [n], --sample=n, the deprecation warning, and the exit-code
  contract (0/1/2/3) are unchanged.

Fixes #237

Validation

• zig build -Dbundle-sqlite=true -Doptimize=ReleaseSafe — pass
• zig build unit-test -Dbundle-sqlite=true — pass
• zig build test -Dbundle-sqlite=true — pass (all integration tests green;
  before the fix the 5 new regression tests failed as expected)
• Manual: printf 'name,age\nAlice,30\nBob,25\nCarol,35\n' | ./zig-out/bin/sql-pipe --inspect sample 2
  prints schema on stderr and header + 2 rows on stdout, exit 0; --inspect=sample 2 same;
  --inspect sample 0 exits 1 with the new diagnostic
• zig fmt --check on tracked *.zig files reports pre-existing violations on master
  (also flagged by CI lint setup); the files touched here are already nonconforming on
  master and none of the reported diffs intersect the new code

Note: GitHub CI does not run the Bash integration suite on Windows; Windows jobs only
compile and run unit tests, so the new CLI cases are verified on Linux/macOS only.