S0318-dicom-7: the second PS3.15 E.3.6 temporal column, the option name that selects it, and MODIFIED

[NSchatz]

Spec: pipeline/active/S0318-dicom-7/spec.md (umbrella).

PS3.15 2026c section E.3.6 specifies two mutually exclusive Retain Longitudinal
Temporal Information Options and Table E.1-1 gives them separate columns. This
package published one option name carrying the full-dates column only, so the
modified-dates branch was unreachable and the third Value of (0028,0303) was
never written. This adds the second column, the second option name, and the
MODIFIED declaration.

What changed

• T1. scripts/generate-annex-e.ts emits Rtn. Long. Modif. Dates Opt. as a
  per-attribute action beside the full-dates one instead of counting its
  divergence and discarding it. The header-label guard already covered both
  temporal indices; it now has a mutation test proving it fires on each.
• T2. RetainLongitudinalTemporalModifiedDates is a second published option
  name. The two temporal options are mutually exclusive and a call naming both
  is refused with the existing INVALID_OPTIONS typed error.
  RetainLongitudinalTemporal keeps its full-dates meaning unchanged.
• T3. (0028,0303) takes MODIFIED on that branch, on the option set alone,
  with the existing single-value replacement behaviour. (0012,0063) gains a
  Value naming the option, inside LO's 64-character per-Value maximum. A new
  stable code DICOM_DEIDENT_DATES_NOT_TRANSFORMED on report.warnings states
  that the run resolved the column and transformed no date; it is never added to
  the parse warnings, so a { strict: true } parse of the same input is
  unaffected.
• T4. The released prose, the release note the prose gate reads, the gate's
  own MODIFIED assertion, the CLAUDE.md line and its agent-notes.md anchor
  all move in the same commits as the behaviour. The locked warning-code
  snapshot moves by hand for the one added code. The locked public-export
  snapshot does not move: this change adds a member to an existing union and an
  entry to an existing frozen array, and no exported name.
• T5. A patch changeset stating the capability with its limitation, and the
  JSDoc on the option surface corrected.

The residual, stated rather than glossed

Section E.3.6 also requires the dates themselves to be modified and the manner
described in a Conformance Statement. Both are permanently the caller's: PS3.2
Annex N scopes a Conformance Statement to a named product and version, which a
library is not. So this library applies the column and writes the declaration,
and the caller performs the transformation. Nothing here claims PS3.15 Annex E
conformance for the Modified Dates Option.

Evidence

• pnpm test:coverage: 86 files, 1680 passed, 1 todo; src/deident and
  src/dictionary both over their per-directory floors, and vitest.config.ts
  is byte-identical to main.
• pnpm gen:all && git diff --exit-code src/dictionary/generated: clean.
• pnpm lint, pnpm typecheck, pnpm format:check, pnpm phi-scan,
  bash scripts/check-no-emdash.sh: all green.
• Every grader was run against a mutation that breaks its property and went red;
  the mutations and their results are recorded in the spec folder's notes.md.