GrantInventoryController reads nonexistent flood config keys and always falls back to defaults

Problem/Motivation

GrantInventoryController reads the configuration keys mint_flood_limit and mint_flood_window from file_gate.settings. Those keys do not exist in the config schema — the real keys are flood_limit and flood_window — so the lookups always return NULL and the controller always applies its hard-coded fallback (50 requests / 60 seconds), regardless of what the site configured.

Low impact: the fallback matches the shipped defaults, so most sites see no difference. A site that tightened or loosened the mint flood settings gets the inventory endpoints throttled at the defaults instead of its configured values — a silent divergence between configuration and behavior.

Steps to reproduce

1. Set flood_limit to a small value (for example 2) in file_gate.settings.
2. Authenticate and call the grants inventory endpoint more than twice within the window.
3. Requests are still allowed up to 50 — the configured limit is not applied on this route (the mint route applies it correctly).

Proposed resolution

Read flood_limit / flood_window (the schema keys) in GrantInventoryController, matching the mint controller. Optionally add a kernel assertion that a configured limit is honored on the inventory route so a renamed key cannot regress silently again.