[PierreRaybaut]

Prepares the merge of develop into the plugin SDK branch by making feature identity explicit and lookups deterministic.

• get_feature(name) no longer depends on registration order: built-in features are preferred, or features from the recorded plugin module when plugin_origin is given (History replay and re-processing pass it). Previously, replaying a plugin feature that shares its name with a built-in feature ran the built-in one.
• Direct compute_1_to_1 calls now honour the registered preview_enabled flag (the lookup used the function name on a registry keyed by function, so it always missed).
• Persisted identities (processing metadata, History) go through a single seam, ComputingFeature.feature_id / BaseProcessor.get_feature_id(). Values are unchanged (function names).
• Removed duplicate Allan/Hadamard registrations and the image transpose "Swap X/Y axes" registration, which no menu reached (the Geometry menu resolves transpose to "Flip diagonally"). No visible change.
• New tests pin built-in identifier uniqueness per panel, lookup preference and preview gating; each fails without the fix.

Full suite: 631 passed, 3 skipped (develop baseline: 628 passed, 3 skipped).

Assisted-by: Claude Opus 5.5