fix(cc-economics): accept ccusage v20 'period' field via serde alias

[Greonzhin]

Problem

rtk cc-economics (and its --daily / --weekly breakdowns) fails with ccusage >= 20:

rtk: Failed to fetch ccusage monthly data: Failed to parse ccusage JSON output:
Invalid JSON structure for monthly data: missing field `month` at line 39 column 5

ccusage v20 switched its root daily / weekly / monthly commands to a unified multi-agent schema where the period-key field is always named period (plus new agent / metadata fields, which serde already ignores):

{ "monthly": [ { "agent": "all", "period": "2026-05", "inputTokens": 15838, "totalCost": 659.17, ... } ] }

src/analytics/ccusage.rs requires date / week / month respectively, so deserialization fails for all three granularities. All other required fields (inputTokens, outputTokens, totalTokens, totalCost) are unchanged in v20.

Fix

Add #[serde(alias = "period")] to the three entry structs. This is backward-compatible: old ccusage versions still emit date / week / month, new ones emit period, and the two never appear together.

Verification

• Reproduced on rtk 0.42.4 and dev-0.44.0-rc.308 with ccusage 20.0.14 (pnpm global, Windows 11).
• Verified the equivalent field-mapping end-to-end on the same machine via a PATH shim that routes rtk's exact invocations to ccusage claude <granularity> (which still emits the legacy field names): cc-economics, --daily, --weekly, and --all all render correctly with the legacy names mapped.
• Note: this branch is not compiled locally (no Rust toolchain on this machine) — the change is attribute-only; CI should verify the build.

🤖 Generated with Claude Code

[CLAassistant]

All committers have signed the CLA.

[aeppling]

Hey @Greonzhin
thanks for this contribution, already solved in #2732