refactor(config): remove legacy ccusage service and deprecated ccotel config

[AnnatarHe]

Summary

Removes legacy config and the ccusage v1 daemon service.

• Deleted model/ccusage_service*.go and its tests. The daemon no longer runs bunx/npx ccusage or posts to /api/v1/ccusage/batch.
• Removed the ccusage config (CCUsage type, field and default). shelltime auth used to write ccusage.enabled: true into every new config.
• Removed the deprecated ccotel field and its silent migration to aiCodeOtel, in both the base and local config.
• Removed a duplicate LogCleanup merge block in mergeConfig.
• Removed the now-unused cmdService from the daemon's main.go.
• Updated docs/CONFIG.md (the legacy section, the proxy note, the example config and the FAQ) and CLAUDE.md.

Behavior note: old configs that still contain ccusage: or ccotel: load fine, because unknown keys are ignored. A config that sets only ccotel: (without aiCodeOtel:) will no longer enable the OTEL collector; rename the key to aiCodeOtel.

Related PRs

• server: https://github.com/shelltime/server/pull/478
• web: https://github.com/shelltime/web/pull/608
• ios: https://github.com/shelltime/ios/pull/169

Test plan

• go build ./...
• go vet ./...: only the cmd/cli/main.go context-cancel warning, which was already there
• go test ./...: model and commands pass. Two daemon socket tests fail locally with bind: invalid argument: the unix socket path built from t.TempDir() and the long test name exceeds macOS's length limit. That package isn't touched here.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	79.19% <ø> (?)

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Files with missing lines	Coverage Δ
model/config.go	94.28% <ø> (-0.35%)	⬇️

... and 2 files with indirect coverage changes

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