fix(store): name the nested Timelines/ layout on >= 8.7 storage (#95)

[renezander030]

Closes #95.

The split

nestedTimelines is populated on every store. The layout value is not — timelines-nested requires !modernStorage, so it stops at 8.7 by design, which is what keeps #50's 7.x claim off modern storage.

Four consumers, two keyed each way:

consumer	keyed off	fires on >= 8.7
cmdDiagnose nested_evidence	nested_timelines.length	yes
capcut fixture bundle	nestedTimelines.length	yes
diagnose next_action	layout	no
version support note	layout	no

So a >= 8.7 project with a nested Timelines/ directory produced a diagnose report carrying nested_timelines and a full redacted nested_evidence block, and not one line of prose in that report said what the structure was. fixture would bundle the exact layout #50 has been blocked on since 2026-08-01 without ever mentioning that the bundle is what's wanted.

The change

NESTED_TIMELINES_MODERN_ACTION, emitted from diagnoseDraftStore and the version command when nested documents exist but the layout is not timelines-nested.

It asserts nothing in either direction. #50 reports 7.x discarding root-mirror edits; #68 reports 8.5.0 regenerating the nested file from the root, byte-identical after a round trip. Both predate the 8.7 storage change and neither transfers across it, so the note names the structure, states that it is unevidenced above 8.7, and ends on the fixture CTA.

Deliberately unchanged

• Write-time stays silent. CapCut 8.5.0 macOS: timelines-nested ingests tool writes; init's template is rejected by the app #60 observed CapCut creating Timelines/<id>/draft_info.json after opening a CLI-written draft, so modern builds produce the directory routinely — a per-write warning would fire for the majority about a hazard nobody has evidenced. That is the timelines-nested write warning is gated on layout, not app version — shows 7.x text to 8.5.0 users #68 failure mode one storage generation later.
• sync-timelines stays silent, same reason.
• Layout taxonomy untouched. No store changes its layout, canonical, or targets.
• Neither existing message is reworded. 7.x keeps CapCut 7.x edits are discarded when the active draft lives under Timelines/ #50's caution, 8.5.0 keeps timelines-nested write warning is gated on layout, not app version — shows 7.x text to 8.5.0 users #68's wording.

Tests

test/timelines-layout.test.mjs, new >= 8.7 storage is named, not asserted block: claim-free diagnose action, matching version note, evidence-and-prose agreement, no false positive without the directory, and exactly one nested note across 7.9.0 / 8.5.0 / 8.7.0 / 9.2.8.

The existing >= 8.7 ... stay silent case is retitled to write silently — it still asserts write-path silence, and its diagnose assertion is tightened from "no action containing discard" to "no action containing may discard those edits", since the new note mentions the word only to disclaim it.

812/812 green, lint clean.