feat(canon): §2.G strip UPGRADE_BASE_VERSION entirely (plausible verified dynamic-base green)

Gate satisfied — live: with the pin removed, plausible's upgrade tier resolves base 3.0.1+v2.0.0 via
the same-version step-back (canonical 3.1.0 == head 3.1.0 → newest-older = 3.0.1, NOT the broken
3.0.0) and passes install+upgrade green (level 5/5). The pin is redundant, so removed everywhere:
- meta.py KEYS entry (RecipeMeta field auto-drops; 15→14 keys).
- run_recipe_ci.resolve_upgrade_base override branch + docstrings.
- tests/unit/test_meta.py (count 15→14, dropped None-assert), test_upgrade_base.py (override test).
- docs/recipe-customization.md (regenerated table + mentions), docs/testing.md.
- tests/plausible/recipe_meta.py (pin removed), tests/bluesky-pds (re-enable note → dynamic base).
294 unit tests pass; lint clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/bluesky-pds/recipe_meta.py

@@ -13,12 +13,13 @@ HTTP_TIMEOUT = 600
 # as an upgrade base anymore: the base crash-loops MODULE_NOT_FOUND before the PR head is ever
 # exercised (phase bsky root cause; cc-ci-plan/upstream/bluesky-pds.md). Declared intentional
 # until a fixed exact-pinned version (0.3.0+v0.4.219, mirror PR #2) is merged AND published —
-# then DROP this and set UPGRADE_BASE_VERSION = "0.3.0+v0.4.219" so the upgrade rung is
-# exercised again from the first deployable base.
+# then DROP this EXPECTED_NA and the upgrade rung resolves its base DYNAMICALLY (phase prevb:
+# last-green warm canonical → same-version step-back → main tip), no explicit pin needed
+# (UPGRADE_BASE_VERSION was removed in phase canon §2.G).
 EXPECTED_NA = {
     "upgrade": "no deployable upgrade base: every published version pins the moving tag "
     "pds:0.4, which upstream republished with incompatible main builds (index.js removed) — "
-    "re-enable via UPGRADE_BASE_VERSION once a fixed version is published post-merge",
+    "drop this once a fixed version is published post-merge (dynamic base then resolves it)",
 }
 
 # canon §2.B: enroll as a DATA-WARM canonical (all recipes enrolled — operator 2026-06-17).