GS: Managed spreadsheet layout and manual refresh route

Parent: #398
Depends on: #400

Design:

• docs/design/google-sheets/architecture.md
• docs/design/google-sheets/spreadsheet-layout.md
• docs/design/google-sheets/authentication.md

Scope

Create and attach the managed control/data/state worksheets, developer metadata, refresh hyperlink, focused refresh route, authentication-intent restoration, and destination verification.

Acceptance criteria

• Linked spreadsheets use stable numeric sheet IDs plus developer metadata.
• The control sheet exposes refresh/status/source actions without secrets.
• _ASB_STATE and staging sheets are hidden and validated as untrusted input.
• Refresh URLs contain only an opaque binding ID in the fragment.
• Opening the link serves the ordinary SPA and resumes after ClickHouse authentication.
• Google authorization is requested explicitly and edit access is verified.
• Renaming or moving a spreadsheet does not break identity.
• A copied spreadsheet is detected and offers explicit relink/remove/cancel choices.
• SQL Browser never identifies resources by sheet name alone.

Non-goals

Query upload/publication semantics, scheduled refresh, or inbound Google callbacks.

Start by reading docs/design/google-sheets/architecture.md, docs/design/google-sheets/spreadsheet-layout.md, and docs/design/google-sheets/authentication.md, then review parent #398 and dependency #400. Done means implementing the listed managed-sheet, refresh-route, authentication, identity, and copied-spreadsheet behaviors while meeting every acceptance criterion and excluding the stated non-goals.