fix(share): allow explicit short links for small plans (#1475)

* fix(share): offer short links for small plans

Fixes #1427. Make short-link creation available for every shareable small plan while preserving explicit uploads, immutable pastes, and current-content encryption.

* fix(storage): resolve data directory when reading and writing

Resolve plan and history paths from the active data-directory configuration instead of capturing a temporary test override at import time. This reproduces and fixes the four order-dependent annotate CI failures reported in #1464; keep both successful persistence and failed-write draft recovery assertions intact.

* test(share): eliminate hydration flake in short URL lifecycle tests

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Co-authored-by: Michael Ramos <support@plannotator.ai>