Map CLI agents directly to stable telemetry strings

[warp-agent-staging]

Description

Replace CLIAgentType with an exhaustive CLIAgent::telemetry_name() mapping so Rust variant names can change without changing analytics values.

Keep CLIAgent and Option<CLIAgent> throughout all telemetry events and emitters. Convert to static strings only in outbound payloads and field serializers, including notifications and code review. Preserve all 19 values, including Cursor, optional/null fields, and the nested notification key c_l_i_agent. Leave CLIAgent serde and session-sharing serialization unchanged. Notification telemetry is outbound-only and implements Serialize, not Deserialize.

Linked Issue

Approved request; no tracked issue or spec for this scoped refactor.

• The linked issue is labeled ready-to-spec or ready-to-implement. Not applicable; implementation was approved directly.
• Where appropriate, screenshots or a short video of the implementation are included below (especially for user-visible or UI changes). Not applicable; telemetry-only change.

Testing

• cargo check -p warp --tests --locked — passed; existing test targets compile.
• cargo clippy -p warp --all-targets --tests --locked -- -D warnings — passed.
• ./script/format and git diff --check — passed.

No new tests: this representation-only refactor preserves emitted behavior. No tests were executed in this validation pass. Checks ran on Linux; cross-platform/workspace CI remains unverified.

• I have manually tested my changes locally with ./script/run. Not applicable; no rendered behavior changed.

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-NONE

[warp-agent-staging]

This PR was generated with Warp.

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