Drop articles before domain nouns for rename safety

[dadachi]

Summary

• Apply the substrate rename-safety contract: remove a / an / the directly preceding Shop, Shopkeeper, and ItemTag (any case form) so the agent's text-only rename pipeline can't produce article disagreements like "an patient" or "a office" when users pick consonant- or vowel-starting rename targets.
• Touches test descriptors (rule 4), code comments (rule 6), OpenAPI endpoint summaries (rule 1, scanned by the rename pipeline as .yaml), and substrate meta-docs.
• No app code, locales, or model strings needed changes — the substrate was already mostly contract-compliant outside docs/ and test/.

Changes

• Test descriptors (7): test/controllers/api/v1/shopkeeper/{item_tags,shops}_controller_test.rb, test/models/shop_test.rb
• Comments (2): test/controllers/api/v1/shopkeeper/base_controller_test.rb, test/models/accounts_invitation_test.rb
• OpenAPI summaries (12): docs/openapi.yaml
• Substrate meta-docs (7): docs/phase1-rails-api.md, docs/nativeapptemplate-substrate-v2-overview.md

Test plan

• bin/rubocop — 227 files inspected, no offenses
• bin/rails test — 398 runs, 815 assertions, 0 failures, 0 errors, 0 skips
• Spot-check rename pipeline output for an ItemTag → Patient (consonant) substitution and confirm no "an patient" / "an Patient" leaks remain

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