docs(rtm): add #833 zeitstrahl-visual-fidelity REQ-001..016 rows

Trace the visual-fidelity requirements end to end before implementation,
matching the timeline-feature convention of landing RTM rows in the first
commit of the branch. Status: Planned; flipped to Done as each task lands.

Refs #833
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.specify/rtm.md

@@ -123,3 +123,19 @@
 | REQ-015 | absent/empty/non-UUID originPersonId → redirect /zeitstrahl (CWE-601) | #781 | timeline-curator-forms | `frontend/src/lib/timeline/eventFormServer.ts#resolveNavTarget` | `new/page.server.spec.ts#defaults to /zeitstrahl when originPersonId is not a valid UUID`, `#redirects to /persons/{id} when originPersonId is a valid UUID` | Done |
 | REQ-016 | title/description/chip labels via default `{...}` escaping, never `{@html}` (CWE-79) | #781 | timeline-curator-forms | `frontend/src/lib/timeline/EventForm.svelte` | code review + `grep -r '@html' frontend/src/lib/timeline/` → zero | Done |
 | REQ-017 | labelled pickers, visible empty states, ≥44px chip remove targets | #781 | timeline-curator-forms | `frontend/src/lib/person/PersonMultiSelect.svelte`, `document/DocumentMultiSelect.svelte`, `EventForm.svelte` | `PersonMultiSelect.svelte.spec.ts`, `DocumentMultiSelect.svelte.spec.ts` (green post-44px fix), `EventForm.svelte.spec.ts#preselects a person when initialPersons is provided` | Done |
+| REQ-001 | `/zeitstrahl` wraps the timeline in a `.tl-canvas` frame (border, rounded, bg-canvas, semantic tokens) | #833 | zeitstrahl-visual-fidelity | `frontend/src/routes/zeitstrahl/+page.svelte` | `routes/zeitstrahl/page.svelte.spec.ts` | Planned |
+| REQ-002 | meta sub-line: range + letter count + event count (years + undated) + "Gruppierung: Datum"; range/line omitted when empty | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/timelineMeta.ts`, `frontend/src/routes/zeitstrahl/+page.svelte` | `timelineMeta.spec.ts`, `routes/zeitstrahl/page.svelte.spec.ts` | Planned |
+| REQ-003 | year badge centered on axis ≥1024px, left spine <1024px; sticky top:4rem preserved | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/YearBand.svelte` | `YearBand.svelte.spec.ts` | Planned |
+| REQ-004 | year badge node marker on the spine, never overlapping the badge text (desktop + phone) | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/YearBand.svelte` | `YearBand.svelte.spec.ts` | Planned |
+| REQ-005 | per-letter connector dot (white fill, mint ring) on the spine; phone column indented clear of card | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/YearBand.svelte` | `YearBand.svelte.spec.ts` | Planned |
+| REQ-006 | axis gradient 3-stop mint→navy→slate via `--palette-mint`/`--palette-navy`/`--c-tag-slate` | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/TimelineView.svelte` | `TimelineView.svelte.spec.ts` (+ REQ-013 grep) | Planned |
+| REQ-007 | EventPill subtitle `{date} · {provenance}` keyed off `entry.derived` (abgeleitet/kuratiert) | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/EventPill.svelte` | `EventPill.svelte.spec.ts` | Planned |
+| REQ-008 | LetterCard title prefixed with `aria-hidden` ✉ + sr-only "Brief"; href intact | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/LetterCard.svelte` | `LetterCard.svelte.spec.ts` | Planned |
+| REQ-009 | WorldBand inline "· historisch" descriptor (non-RANGE & RANGE); RANGE span pill + aria-label intact | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/WorldBand.svelte` | `WorldBand.svelte.spec.ts` | Planned |
+| REQ-010 | YearLetterStrip count ✉ + sr-only label + "Monats-Dichte" caption; expand toggle preserved | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/YearLetterStrip.svelte` | `YearLetterStrip.svelte.spec.ts` | Planned |
+| REQ-011 | YearLetterStrip exactly two endpoint month-axis labels (Jan/Dez {year}) ≥10px via formatTickLabel | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/YearLetterStrip.svelte` | `YearLetterStrip.svelte.spec.ts` | Planned |
+| REQ-012 | undated "Ohne Datum · {count}" in a dashed frame; empty → absent; kind/type dispatch preserved | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/TimelineView.svelte` | `TimelineView.svelte.spec.ts` | Planned |
+| REQ-013 | all new styles use semantic tokens; corrected hex grep returns zero hits | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/*` | grep gate (REQ-013 form) → zero | Planned |
+| REQ-014 | no change to DTO order, density threshold (12), gap-folding, or ol/section/h2 structure | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/*` | existing timeline + `zeitstrahl/page.server.test.ts` suites stay green | Planned |
+| REQ-015 | new user-facing strings are Paraglide keys present in de/en/es with matching key sets | #833 | zeitstrahl-visual-fidelity | `frontend/messages/{de,en,es}.json` | `messages.spec.ts` | Planned |
+| REQ-016 | LetterCard with no title → no ✉, no sr-only "Brief"; sender→receiver + date still render | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/LetterCard.svelte` | `LetterCard.svelte.spec.ts` | Planned |