fix: wire elicitation into platform config providers

[Muizzkolapo]

Summary

• Introduce CredentialsProviderProtocol so platform config providers accept both CredentialsProvider and ElicitingCredentialsProvider
• Make _is_multi_project() sync — reads settings.dbt_project_ids directly instead of calling get_credentials(), eliminating the 17-second hang in Cursor ([Bug]: Cursor - v1.17.1 No tools, prompts, or resources #759)
• Wire ElicitingCredentialsProvider to platform config providers (discovery, semantic layer, admin API) gated on settings.any_platform_toolset_active, so elicitation fires when a platform tool is called without DBT_HOST
• CLI-only users (DBT_MCP_ENABLE_DBT_CLI=true) are fully isolated from platform concerns

Test plan

• list_tools() returns instantly with no credential fetch or OAuth
• Calling a platform tool without DBT_HOST triggers elicitation wizard
• CLI-only mode sees no wizard and no platform errors
• Proxied tools stay on raw credentials (no elicitation at lifespan time)
• Cached credentials on second call (no re-elicitation, no re-OAuth)
• 660 unit tests pass

Fixes #762
Root-causes #759

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Detect platform tools enabled via DBT_MCP_ENABLE_TOOLS

In allowlist mode, any_platform_toolset_active is entered when enable_tools is set, but this branch only checks enable_* toolset flags and ignores individually enabled tools from DBT_MCP_ENABLE_TOOLS. That means configs that enable a platform tool by name (without setting DBT_MCP_ENABLE_DISCOVERY/_SEMANTIC_LAYER/etc.) are misclassified as “no platform toolsets active”, so load_config() injects raw CredentialsProvider into platform providers and platform calls fail with MissingHostError instead of triggering elicitation.

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