Land T1.25b: text times by a fixed list of formats

The pandas emulation in sdm-engine::time::text is replaced by jiff
strtime parsing of a fixed, documented list of formats (ISO 8601 / RFC
3339 and the client two shapes, date-rules.md), with the client
documented day/month and two-digit-year rules; everything else is
refused by name (text_time), an open order as text_time_order, years
outside 1..9999 refused. Spec vectors recorded without pandas; a
differential report classifies every change. DT-15 approved (owner
T1.25b answer), DT-16 and DT-17 approved by the owner 2026-10-11, DT-6
withdrawn. text.rs 884 to 624 lines. The dead floor-cell waiver removed.
E68. 3 review rounds, 1 fix round.

Candidate run 38255383371 green at
37bda41; this commit changes no file,
so the phase branch moves at once and its own runs are recorded
afterwards (E43 (b)).

Reviewed-by: independent reviewer (fresh agent) and Codex, T1.25b
Protected-paths: .github/workflows/ci.yml; contract/protected-paths.txt; docs/design/rust-core/register.yaml; packages/structured-data-models-client/tests/test_the_schema_route.py; rust/crates/sdm-engine/tests/text-times-differential.json; rust/crates/sdm-engine/tests/text-times.json; rust/crates/sdm-engine/tests/text_times.rs; rust/crates/sdm-engine/tests/text_times_record.py; tests/test_contract_ci_gate.py
Base-SHA: de247a3
Checkpoint-SHA: de247a3
Signed-off-by: Adi Wadaskar <awadaskar@nvidia.com>

Author: adi-kumo