fix(share_plus): avoid iOS 26 share sheet crash for non-image files

[MohamedAbdallah-14]

Fixes #3784.

What's wrong

Pre-iOS 26 the plugin used a fake file URL trick to display the file size and extension as a subtitle in the iOS share sheet:

// description = "DOCX • 500 KB"
metadata.originalURL = [NSURL fileURLWithPath:description];

This worked because pre-iOS 26 versions of LinkPresentation accepted any NSURL and only used it for display lookup.

iOS 26 tightened validation of LPLinkMetadata.originalURL. When SHSheetActivityItemsManager asynchronously fetches link metadata for the bogus URL — reproducible when sharing .docx files — LPLinkPreview returns a nil or incomplete metadata object, and _updateMetadataItemForActivityItem:withFetchedMetadata: crashes inserting it into an NSMutableArray:

*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil
SHSheetActivityItemsManager -[SHSheetActivityItemsManager _updateMetadataItemForActivityItem:withFetchedMetadata:]
SHSheetActivityItemsManager -[SHSheetActivityItemsManager _fetchMetadataForActivityItem:withHandler:]

Fix

Gate the fake-URL trick on iOS < 26 with @available(iOS 26.0, *). On iOS 26 and later, leave originalURL unset (defaults to nil). The share sheet still works — the title and image preview both still render — but the size/extension subtitle that the fake URL was producing is no longer shown on iOS 26+.

That tradeoff matches what the reporter on #3784 already suggested:

Setting metadata.originalURL = nil instead of the fake path may help.

PDFs and plain text are unaffected, and pre-iOS 26 behaviour is unchanged.

Test plan

• Manually verify on an iOS 26.x device or simulator: share a .docx file, confirm no crash.
• Manually verify on an iOS 17 device or simulator: share a .docx file, confirm subtitle still shows ("DOCX • 500 KB").
• Manually verify on iOS 17 and iOS 26: image sharing still produces a thumbnail preview (metadata.imageProvider path is unaffected).

I do not currently have an iOS 26 simulator to run the repro myself; opening as a draft so a maintainer or CI can validate the iOS 26 behaviour before this is marked ready.

Risks

• iOS 26+ users lose the file size subtitle in the share sheet. The title and image preview are unaffected. This matches the reporter's expectation in the issue.
• If a future iOS version reintroduces support for arbitrary originalURL values, this gate could be removed; for now iOS 26.0 is the safe lower bound based on the reproduction in [Bug]: share_plus iOS 26 crash — NSArrayM insertObject:atIndex: nil object in SHSheetActivityItemsManager when sharing DOCX files #3784.

Related

• [Bug]: Avoid crash on iOS 26 on iPhones with no sharePositionOrigin #3768 — separate iOS 26 crash with sharePositionOrigin (PR fix(share_plus): avoid crash on iOS 26 on iPads with no sharePosition… #3769).
• [Bug]: iOS 26 Unhandled Exception: PlatformException(error, sharePositionOrigin: argument must be set, {{0, 0}, {0, 0}} must be non-zero and within coordinate space of source view: {{0, 0}, {414, 896}}, null, null) #3645 — sharePositionOrigin must be set crash.

[MohamedAbdallah-14]

The Android API 36 job timed out waiting for the emulator to boot (Timeout waiting for emulator to boot at the getprop sys.boot_completed polling step) — it never reached the test phase. Fail-fast then cancelled API 32, API 29, and the iOS job before they could run.

This PR is iOS-only (FPPSharePlusPlugin.m); no Android code is touched. Could you re-run the failed jobs when you get a chance? The iOS integration test in particular needs to actually execute to validate the fix.