[Shared Utils & Models] Add retry usage examples and initial adoption sweep

[saviornt]

Description

After retry helpers are created and used in MQTT factory, add documentation examples and do a small proactive sweep to apply them in obvious places (Omada polling, Netmiko, etc.).

Type

• Epic
• Feature
• Task
• Bug
• Refactor
• Research
• Documentation
• Setup / Tooling

Focus Area (pick one)

• Monorepo & Packaging
• Appliance Core (Pi edge)
• Assistant Core (PC central)
• Shared Utils & Models
• Auth & Security
• MQTT & Comms
• Dashboard & UI
• Observability & Metrics
• Inference & ML
• Testing & CI
• Documentation & Planning

Priority

• Critical
• High
• Medium
• Low

Acceptance Criteria

List the specific, testable outcomes that mean this issue is done.

• shared/README.md or dedicated retry.md documents at least 3 usage patterns
• At least 2–3 additional call sites updated to use retry decorators (examples: Omada API poll loop, initial Netmiko connect)
• All changes pass MyPy, tests, linting
• No behavioral change in non-transient failure cases

Blocker / Dependencies

• Both previous retry-related issues must be completed

Notes / Links

• This is a "polish" issue — can be done after core retry is working