feat(newos4): mobile download/share UX — deferred blob revoke, multi-select, Web Share, 44px targets

Executes .hermes/plans/2026-10-24_051600-newos4-mobile-download-share.md (approved via the feedback
dashboard; marker autonomy: safe). Front-end only, v4.6.94 -> v4.6.95.

T1 modules/ext/filemgr.js — URL.revokeObjectURL ran in the same tick as a.click(); iOS Safari and
   Android Chrome hand the blob: URL to the download manager asynchronously, so the transfer was
   aborted while the status line still said "Downloaded". Now revoked after 30 s.
T2 download honours the multi-selection via _getSelectedPaths() (falling back to _selectedFile),
   reports "⬇ Downloaded N files" and "❌ Skipped <path>" instead of a silent partial success.
T3 share: navigator.share -> clipboard.writeText -> inline read-only <input> (focused, selected).
   prompt() is suppressed in iOS standalone PWAs and most Android WebViews, which is why tapping 🔗
   did nothing. Unresolvable space now reports "🔗 Share unavailable — no space resolved".
T4 both preview toolbar buttons: min-height/min-width 44px, touch-action manipulation, 1em, gap 10px
   (was 24px/0.85em/6px — the smallest tap targets in the UI).
T5 _previewShareUrl falls back _resolveSpaceName -> _detectSpaceName (webdav.js:22) -> page path,
   and returns null rather than emitting /spaces//<path>.
T6 the URL helpers are now module-scope pure functions exported for Node, so
   modules/test/test-download-url.js tests the shipped code instead of a local copy (4 -> 6 cases).
   Also fixes a latent bug that made require() impossible: `typeof window.webx11` throws under Node
   because typeof does not protect a member access on an undefined global.

Verified on the served bundle (filemgr.js is concatenated into critical-ext-bundle.js, NOT
core-bundle.js — the plan's T7 grep pointed at the wrong file): HTTP 200, 129 867 B, 2x
navigator.share, 3x fmBuildShareUrl, deferred revoke present, 11x min-height:44px.
Live browser probe on /spaces/newos4/main.html: _previewShareUrl('docs/a.md') ->
https://webx11.duckdns.org/spaces/newos4/docs/a.md (no double slash); with navigator.share absent
and clipboard blocked, clicking 🔗 produced .fm-share-input containing that URL; button style ends
min-height:44px;min-width:44px;touch-action:manipulation; toolbar gap:10px.
node modules/test/test-download-url.js -> 6 PASS. lint-no-undef clean (55 files).
maintain: PASS version v4.6.95 x3, syntax OK, HTTP 200 /main.html.

Also adds admin/docs/session-overview-2026-10-26.md (glm-5.3-compressed session record).

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