refactor: update workflow with new pcl command

[lean-apple]

Ref ENG-2236

Updates PCL documentation to reflect the new declarative pcl apply workflow, replacing the old imperative pcl store + pcl submit flow.

• pcl apply is now the primary deployment command: CLI reference, quickstart tutorial, and a new dedicated guide (apply-assertions.mdx) all walk
  users through the credible.toml + pcl apply flow
• pcl store and pcl submit fully removed from docs: All references, examples, and the old store-submit-assertions.mdx page are gone
• "Dapp" → "Platform": Renamed in all text content and mermaid diagrams
• Auth methods expanded: Docs now reference all supported auth methods — wallet, email, Google, and GitHub
• Release vs deploy distinction: Clarified that pcl apply creates a release; you then review and deploy in the platform to activate assertions
• Ownership note added: Account must be linked to the wallet that owns the contracts on-chain
• pcl build no longer a separate step: Removed from workflows since pcl apply builds automatically
• Assertion DA is platform-managed: Users no longer interact with DA directly — pcl apply handles it
• Architecture diagrams updated: Mermaid flows now show CLI → Platform → DA instead of CLI → DA + CLI → Dapp

[linear]

ENG-2236 docs(pcl): update documentation for declarative pcl apply workflow