Extension framework P1 core primitives (P1-1..P1-4)

[jongio]

Parent: #6853
Related: #6855, #6856

Objective

Implement P1 foundational primitives that unblock the rest of extension framework improvements.

Proposal IDs covered

• P1-1 Framework Token Provider
• P1-2 URL-to-scope detection
• P1-3 Framework HTTP client with resilience
• P1-4 Pagination support

In scope

• Define stable additive API contracts for all four primitives.
• Implement production-ready behavior with predictable defaults.
• Add unit + edge-case tests and examples for extension authors.

Out of scope

• Key Vault gRPC integration and config helpers (handled in Extension framework P1 integration helpers (P1-5..P1-6) #6945).
• P2/P3 utility families.

Dependencies

• No hard dependency on other open workstreams.
• Should land before Extension framework P1 integration helpers (P1-5..P1-6) #6945 to reduce rework.

Deliverables

• Token provider helper API + implementation + tests.
• URL-to-scope detector + tests for known endpoint classes.
• Resilient HTTP client helper + timeout/retry/backoff tests.
• Pagination abstraction + tests across success/empty/error paths.
• Usage examples and migration notes.

Verification checklist

• Additive/non-breaking API surface.
• Failure handling is explicit (no silent fallback behavior).
• mage preflight passes.

Definition of done

• P1-1..P1-4 are complete, tested, and documented.