chore(release): beta packaging — signing, changelog, store metadata, scale test

- Android release signing reads a gitignored key.properties, falling back
  to debug keys so contributors can still build --release.
- CHANGELOG.md (human, newest-first) + Fastlane/F-Droid metadata (en/es)
  with descriptions derived from docs/intro.md.
- docs/release.md: the by-hand build + manual smoke checklist (no CI yet).
- inventory_scale_test guards the list query against N+1 at 3000 varieties.

apps/app_seeds/fastlane/metadata/android/en-US/full_description.txt

@@ -0,0 +1,27 @@
+Tanemaki (種まき, "to sow seeds") is a local-first, decentralized app for
+keeping and sharing traditional seeds.
+
+Every traditional seed is a letter written by thousands of generations, passed
+from hand to hand. Tanemaki helps people and seed-saver collectives keep a
+friendly inventory of their bank, decide what they offer, and share it locally
+— without a central intermediary that could control, censor, or be fined for
+it.
+
+MANAGE YOUR BANK
+• Add a seed with just a photo and a name — no Latin required.
+• Note the year, how much you have, where it came from, germination tests.
+• Search and filter; snap a photo now and name it later.
+
+YOURS, AND ONLY YOURS
+• Works fully offline. No account, no server, no trackers.
+• Everything is encrypted at rest on your device.
+• Save an encrypted backup and keep a printed recovery sheet — restore your
+  whole bank on a new device.
+
+SHARE, THE WAY IT'S ALWAYS BEEN DONE
+• Mark what you have spare to give away, swap or sell.
+• Print a catalog of what you share to take to a seed fair.
+
+Tanemaki is free software (AGPL-3.0). No ads, no commissions, no business model
+— it exists to support traditional varieties and push back against the seed
+monopoly.