route: add --desc flag to create/update (doc-vs-code mismatch)

[shreemaan-abhishek]

Found during Run 2 smoke testing (see docs/ga-test-report.md).

Problem

README documents:

a7 route update <id> --name my-route --desc "Updated route for API v1"

but ./bin/a7 route create --help and ./bin/a7 route update --help do not expose a --desc flag. The description is only settable through -f file.

Fix

Add --desc to both pkg/cmd/route/create/create.go and pkg/cmd/route/update/update.go (with the corresponding Desc field handling). Mirror how consumer create / service create already accept --desc.

Tests

Bug-protocol: write a failing E2E first, then fix. Suggested:

• TestRoute_CreateWithDescFlag: create with --desc X, get back, assert desc == X
• TestRoute_UpdateDescFlag: existing route, update --desc Y, get, assert desc == Y

Part of #22.