geolocation/cli: show codes instead of pubkeys in user get and probe get

[ben-dz]

Summary of Changes

• geolocation user get: the Targets table probe column now shows the human-readable probe code instead of the raw geoprobe pubkey, resolved via list_geo_probes with a pubkey fallback. JSON gains a probe code field while retaining the canonical geoprobe_pk.
• geolocation probe get: the exchange field now shows the exchange code instead of the raw pubkey, resolved via list_exchanges with a pubkey fallback — making it consistent with geolocation probe list, which already does this.

Diff Breakdown

Category	Files	Lines (+/-)	Net
Core logic	2	+25 / -9	+16
Tests	2	+168 / -0	+168
Total	2	+193 / -9	+184

Two small CLI display fixes in the geolocation crate; the bulk of the diff is test coverage for code resolution and pubkey fallback.

Key files (click to expand)

• crates/doublezero-geolocation-cli/src/user/get.rs — resolve geoprobe_pk → probe code in the Targets table; keep geoprobe_pk in JSON, add probe code field; tests for code rendering and fallback
• crates/doublezero-geolocation-cli/src/probe/get.rs — resolve exchange_pk → exchange code, matching probe list; tests for code rendering and fallback

Testing Verification

• user get: table asserts the probe code (ams-probe-01) and not the pubkey; new fallback test when the probe isn't found; compact-JSON test asserts both probe code and retained geoprobe_pk
• probe get: table asserts the exchange code (ams) and not the pubkey; new fallback test when the exchange isn't found; JSON/compact tests updated to expect the code
• All user::get and probe::get tests pass; make rust-lint clean in the dev container