Linter: TTL properties must be renamed to `TimeToLiveIn<Unit>`

Parent: #4442

## Convention

**DO** Consider renaming TTL properties or parameters to `TimeToLiveIn`.

> Source: [Azure SDK for .NET Mgmt Naming Conventions](https://github.com/Azure/azure-sdk-for-net/blob/main/doc/dev/Mgmt-Naming-Conventions.md)

## Observed today

A scan of `Azure/azure-rest-api-specs` (334 `client.tsp` files, 10,754 csharp-scoped `@@clientName` decorators) shows **1** decorators currently encoding this rule by hand. Examples:

- `ttl` → `TimeToLiveInSeconds` (communication/Communication.Management/client.tsp)

## Proposed linter

**Detection**

Flag any property/parameter whose name matches `^ttl$`, `^TTL$`, ends with `Ttl`/`TTL`, or contains `TimeToLive` without an `In` suffix.

**Auto-fix**

Suggest `TimeToLiveInSeconds` (or other unit) via `@@clientName(..., "csharp")`.

**Scope**

The rule should be csharp-scoped — it only flags violations of the .NET convention, not the underlying TypeSpec name. It should suggest inserting a `@@clientName(..., "csharp")` override when the underlying TypeSpec name is intentional, or renaming the TypeSpec model when the convention applies cross-language.

## Acceptance criteria

- [ ] New lint rule registered in the appropriate ruleset (`@azure-tools/typespec-client-generator-core` or `@azure-tools/typespec-azure-resource-manager`).
- [ ] Doc page under `website/src/content/docs/docs/libraries/.../rules/`.
- [ ] Unit tests covering positive / negative cases and the auto-fix.
- [ ] A `.chronus/changes/` entry.

Inspect the existing rulesets in @azure-tools/typespec-client-generator-core and @azure-tools/typespec-azure-resource-manager to choose the registration point. Then review the lint rule tests and the website/src/content/docs/docs/libraries/.../rules/ location before adding positive, negative, and auto-fix coverage. Done means the csharp-scoped rule, documentation, and .chronus/changes/ entry are present.

Written by the indexing model from the issue text.