fix(date): accept HH:MM date-times and zone suffixes in -d

[xmakro]

What changed

date -d now accepts ISO date-times without seconds and with a zone. touch -d and find -newermt share the parser and gain the same forms.

• YYYY-MM-DD HH:MM (with T or a space), and an optional fraction after the seconds
• a trailing UTC/GMT, Z, or a numeric offset (+0200, +02:00, -05), so git's %ci output parses

The change is a few more chrono formats next to the existing ones; chrono validates the fields and the offset range.

Why

Only YYYY-MM-DD and YYYY-MM-DD HH:MM:SS without a zone were accepted, so common inputs such as a minute-precision timestamp, a UTC log line or a git commit date failed with invalid date.

Before / After

$ date -u -d '2026-10-08 14:30' '+%F %T'
Before: date: invalid date '2026-10-08 14:30'
After:  2026-10-08 14:30:00

$ date -u -d '2026-10-08 14:30:15 UTC' '+%F %T'
Before: date: invalid date '2026-10-08 14:30:15 UTC'
After:  2026-10-08 14:30:15

$ date -u -d '2026-10-08 14:30:15 +0200' '+%F %T'
Before: date: invalid date '2026-10-08 14:30:15 +0200'
After:  2026-10-08 12:30:15

Every After line matches GNU date 9.12. Compared with GNU on 31 date-time inputs in UTC and America/Los_Angeles: the only differences are rare forms this still rejects (a comma fraction 14:30:15,5, an exact -2400 offset, 2026-10-08Z), and 12:30:60, which bashkit already accepted before this change.

Risk

• Low
• Inputs that failed before now parse; inputs that parsed before parse the same way.

Checklist

• Tests added or updated: unit tests, spec cases in date.test.sh, three rows in the GNU date differential test
• Backward compatibility considered

Maintainer validation

Synced with current main; added the required knowledge update and shared-parser integration regressions. The contributor's parsing implementation is unchanged.

• Shared date/touch/find regression fails on clean main and passes with this change.
• 62 date unit tests; 14 timezone/shared-parser tests; GNU date 9.12 differential cases; 8 no-tzdata tests: passed.
• Bash specs: 3,952 passed, 0 failed, 28 intentionally skipped.
• End-to-end smoke checks: offsets, fractional/pre-epoch file timestamps, DST gap/fold policy, malformed and bounded-size inputs, path-style TZ isolation, and strict find -newermt comparisons passed.
• cargo fmt --all -- --check, cargo clippy -p bashkit --lib --tests -- -D warnings, OKF and doc-link checks passed.
• Security review: timezone resolution remains sandbox-only; parsing uses fixed chrono formats with no new dependencies, host I/O, network access, unsafe code, or user-derived format strings.

Local full-gate limitation

Full workspace Clippy passed. just pre-pr passed all 3,732 library tests, then aborted on macOS in blackbox_security_tests::finding_nested_cmd_subst_stack_overflow::depth_50_is_bounded (SIGABRT/stack overflow). The same focused test reproduces on clean current main 28a7f0210896462e7a2ba8c7382ab08ee5a23975, with the same workspace feature configuration. This is a pre-existing project failure, not introduced by this date change; the full local gate is therefore not claimed green.

Baseline command: cargo test blackbox_security_tests::finding_nested_cmd_subst_stack_overflow::depth_50_is_bounded -- --exact --nocapture.

Remaining local gates were run separately after the unrelated stack abort: 158 repository-script tests, capability/OKF/doc-link/workflow/changelog checks, and cargo vet --locked passed.

Final CI: all 42 checks passed on reviewed head e260f1e40a7c84e392d9e12e7db7d88edcf1534a.

[chaliy]

Approved reviewed revision e260f1e. No blocking security, correctness, or alignment findings.

The change extends the existing shared date parser, preserving sandbox-only timezone authority, authoritative explicit offsets, and validated chrono formats. No dependency, workflow, host-I/O, network, or unsafe-code changes are introduced relative to current main.

Added the required canonical knowledge update and regressions covering consistent instants across date/touch/find, fractional file timestamps, strict newer-than comparisons, and rejection before file effects. The positive regression fails on clean main and passes with the contribution.

Validation: all 42 CI checks passed on this exact head. Local date unit/timezone tests, GNU date 9.12 differentials, lean-build tests, 3,952 Bash spec cases, full workspace Clippy, 3,732 library tests, 158 repository-script tests, drift checks, and cargo vet passed.

Local full-gate limitation: just pre-pr aborts on macOS in blackbox_security_tests::finding_nested_cmd_subst_stack_overflow::depth_50_is_bounded. The same SIGABRT/stack overflow reproduces on clean main 28a7f02 with the same workspace feature configuration. This predates the contribution; the full local gate is not claimed green. Details and baseline command are recorded in the PR description.