Document the Object Store download permission rule

[AlexCatarino]

Summary

"How do I download my files from the Object Store?" is the most repeated support question with a fixed policy answer. The current Download Files page only says "contact us to unlock this feature", so every tier emails support and most get told no.

• Rewrite Resources/object-store/download-files-from-cloud-permission.php (shared by the Cloud Platform, Organizations, and LEAN CLI Download Files pages) to state the rule up front: Institution tier plus the derived data agreement, not available on the other tiers, storage subscriptions don't change it, the gate covers every file including uploads and algorithm output, raw data is never exportable, and the API/CLI error text Organization does not have derivative export enabled. Lists the in-cloud alternatives (read in Research or a backtest, Download Results, log quota, lean cloud pull for project files). Replaces the broken mailto with the pricing page's demo wording and /appointments link.
• Scope the click-through walkthrough in download-files-from-cloud.php to permissioned organizations and drop the old fallback paragraph (moved into the list above).
• Cross-link from the Institution Tier and Trading Firm Tier pages and from the Storage Sizes table.
• Add a description to /object/get in the OpenAPI spec and regenerate the Get Object Store File reference, which adds a Description page and renumbers Request and Responses (no docs link to those anchors).
• Add download, export, derivative export, institution to both Object Store section keywords.
• Backtesting Results: link each item on Download Results to its section, and note on Runtime Statistics that custom statistics appear in the banner and download with the results, with the limits from Adjust runtime statistics handling Lean#9760 (50 statistics, 200 characters, encoded values ignored, one debug message).

Test plan

• code-generators/API-Reference-Code-Generator.py regenerated only the Get Object Store File folder; Request and Responses are byte-identical to the previous files.
• vacuum lint QuantConnect-Platform-2.0.0.yaml --fail-severity error passes.
• Every /docs/v2/...#anchor in the changed files resolves through doc_anchors.check_section_anchor.
• Lean CLI relays the /object/get errors array verbatim (lean/components/api/api_client.py), so the error text customers quote appears in both the API and CLI.
• Reviewer with a non-permissioned org: confirm what the Download button does on the Object Store page. Tickets report both a disabled button and a "Permissioned Institutional clients" notice; the text says the action "is unavailable" to cover both.
• Confirm "derived data agreement" is the name of the signed document.